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<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">unittest.mock</span></code> — getting started</a><ul>
<li><a class="reference internal" href="#using-mock">Using Mock</a><ul>
<li><a class="reference internal" href="#mock-patching-methods">Mock Patching Methods</a></li>
<li><a class="reference internal" href="#mock-for-method-calls-on-an-object">Mock for Method Calls on an Object</a></li>
<li><a class="reference internal" href="#mocking-classes">Mocking Classes</a></li>
<li><a class="reference internal" href="#naming-your-mocks">Naming your mocks</a></li>
<li><a class="reference internal" href="#tracking-all-calls">Tracking all Calls</a></li>
<li><a class="reference internal" href="#setting-return-values-and-attributes">Setting Return Values and Attributes</a></li>
<li><a class="reference internal" href="#raising-exceptions-with-mocks">Raising exceptions with mocks</a></li>
<li><a class="reference internal" href="#side-effect-functions-and-iterables">Side effect functions and iterables</a></li>
<li><a class="reference internal" href="#mocking-asynchronous-iterators">Mocking asynchronous iterators</a></li>
<li><a class="reference internal" href="#mocking-asynchronous-context-manager">Mocking asynchronous context manager</a></li>
<li><a class="reference internal" href="#creating-a-mock-from-an-existing-object">Creating a Mock from an Existing Object</a></li>
<li><a class="reference internal" href="#using-side-effect-to-return-per-file-content">Using side_effect to return per file content</a></li>
</ul>
</li>
<li><a class="reference internal" href="#patch-decorators">Patch Decorators</a></li>
<li><a class="reference internal" href="#further-examples">Further Examples</a><ul>
<li><a class="reference internal" href="#mocking-chained-calls">Mocking chained calls</a></li>
<li><a class="reference internal" href="#partial-mocking">Partial mocking</a></li>
<li><a class="reference internal" href="#mocking-a-generator-method">Mocking a Generator Method</a></li>
<li><a class="reference internal" href="#applying-the-same-patch-to-every-test-method">Applying the same patch to every test method</a></li>
<li><a class="reference internal" href="#mocking-unbound-methods">Mocking Unbound Methods</a></li>
<li><a class="reference internal" href="#checking-multiple-calls-with-mock">Checking multiple calls with mock</a></li>
<li><a class="reference internal" href="#coping-with-mutable-arguments">Coping with mutable arguments</a></li>
<li><a class="reference internal" href="#nesting-patches">Nesting Patches</a></li>
<li><a class="reference internal" href="#mocking-a-dictionary-with-magicmock">Mocking a dictionary with MagicMock</a></li>
<li><a class="reference internal" href="#mock-subclasses-and-their-attributes">Mock subclasses and their attributes</a></li>
<li><a class="reference internal" href="#mocking-imports-with-patch-dict">Mocking imports with patch.dict</a></li>
<li><a class="reference internal" href="#tracking-order-of-calls-and-less-verbose-call-assertions">Tracking order of calls and less verbose call assertions</a></li>
<li><a class="reference internal" href="#more-complex-argument-matching">More complex argument matching</a></li>
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<section id="unittest-mock-getting-started">
<h1><code class="xref py py-mod docutils literal notranslate"><span class="pre">unittest.mock</span></code> — getting started<a class="headerlink" href="#unittest-mock-getting-started" title="Link to this heading"></a></h1>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.3.</span></p>
</div>
<span class="target" id="getting-started"></span><section id="using-mock">
<h2>Using Mock<a class="headerlink" href="#using-mock" title="Link to this heading"></a></h2>
<section id="mock-patching-methods">
<h3>Mock Patching Methods<a class="headerlink" href="#mock-patching-methods" title="Link to this heading"></a></h3>
<p>Common uses for <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate"><span class="pre">Mock</span></code></a> objects include:</p>
<ul class="simple">
<li><p>Patching methods</p></li>
<li><p>Recording method calls on objects</p></li>
</ul>
<p>You might want to replace a method on an object to check that
it is called with the correct arguments by another part of the system:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">real</span> <span class="o">=</span> <span class="n">SomeClass</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">real</span><span class="o">.</span><span class="n">method</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s1">&#39;method&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">real</span><span class="o">.</span><span class="n">method</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="n">key</span><span class="o">=</span><span class="s1">&#39;value&#39;</span><span class="p">)</span>
<span class="go">&lt;MagicMock name=&#39;method()&#39; id=&#39;...&#39;&gt;</span>
</pre></div>
</div>
<p>Once our mock has been used (<code class="docutils literal notranslate"><span class="pre">real.method</span></code> in this example) it has methods
and attributes that allow you to make assertions about how it has been used.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>In most of these examples the <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate"><span class="pre">Mock</span></code></a> and <a class="reference internal" href="unittest.mock.html#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate"><span class="pre">MagicMock</span></code></a> classes
are interchangeable. As the <code class="docutils literal notranslate"><span class="pre">MagicMock</span></code> is the more capable class it makes
a sensible one to use by default.</p>
</div>
<p>Once the mock has been called its <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.called" title="unittest.mock.Mock.called"><code class="xref py py-attr docutils literal notranslate"><span class="pre">called</span></code></a> attribute is set to
<code class="docutils literal notranslate"><span class="pre">True</span></code>. More importantly we can use the <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.assert_called_with" title="unittest.mock.Mock.assert_called_with"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assert_called_with()</span></code></a> or
<a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.assert_called_once_with" title="unittest.mock.Mock.assert_called_once_with"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assert_called_once_with()</span></code></a> method to check that it was called with
the correct arguments.</p>
<p>This example tests that calling <code class="docutils literal notranslate"><span class="pre">ProductionClass().method</span></code> results in a call to
the <code class="docutils literal notranslate"><span class="pre">something</span></code> method:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">ProductionClass</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">method</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">something</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">something</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">,</span> <span class="n">c</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">pass</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">real</span> <span class="o">=</span> <span class="n">ProductionClass</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">real</span><span class="o">.</span><span class="n">something</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">real</span><span class="o">.</span><span class="n">method</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">real</span><span class="o">.</span><span class="n">something</span><span class="o">.</span><span class="n">assert_called_once_with</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
</pre></div>
</div>
</section>
<section id="mock-for-method-calls-on-an-object">
<h3>Mock for Method Calls on an Object<a class="headerlink" href="#mock-for-method-calls-on-an-object" title="Link to this heading"></a></h3>
<p>In the last example we patched a method directly on an object to check that it
was called correctly. Another common use case is to pass an object into a
method (or some part of the system under test) and then check that it is used
in the correct way.</p>
<p>The simple <code class="docutils literal notranslate"><span class="pre">ProductionClass</span></code> below has a <code class="docutils literal notranslate"><span class="pre">closer</span></code> method. If it is called with
an object then it calls <code class="docutils literal notranslate"><span class="pre">close</span></code> on it.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">ProductionClass</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">closer</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">something</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">something</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="gp">...</span>
</pre></div>
</div>
<p>So to test it we need to pass in an object with a <code class="docutils literal notranslate"><span class="pre">close</span></code> method and check
that it was called correctly.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">real</span> <span class="o">=</span> <span class="n">ProductionClass</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">real</span><span class="o">.</span><span class="n">closer</span><span class="p">(</span><span class="n">mock</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">close</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">()</span>
</pre></div>
</div>
<p>We don’t have to do any work to provide the ‘close’ method on our mock.
Accessing close creates it. So, if ‘close’ hasn’t already been called then
accessing it in the test will create it, but <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.assert_called_with" title="unittest.mock.Mock.assert_called_with"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assert_called_with()</span></code></a>
will raise a failure exception.</p>
</section>
<section id="mocking-classes">
<h3>Mocking Classes<a class="headerlink" href="#mocking-classes" title="Link to this heading"></a></h3>
<p>A common use case is to mock out classes instantiated by your code under test.
When you patch a class, then that class is replaced with a mock. Instances
are created by <em>calling the class</em>. This means you access the “mock instance”
by looking at the return value of the mocked class.</p>
<p>In the example below we have a function <code class="docutils literal notranslate"><span class="pre">some_function</span></code> that instantiates <code class="docutils literal notranslate"><span class="pre">Foo</span></code>
and calls a method on it. The call to <a class="reference internal" href="unittest.mock.html#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch()</span></code></a> replaces the class <code class="docutils literal notranslate"><span class="pre">Foo</span></code> with a
mock. The <code class="docutils literal notranslate"><span class="pre">Foo</span></code> instance is the result of calling the mock, so it is configured
by modifying the mock <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.return_value" title="unittest.mock.Mock.return_value"><code class="xref py py-attr docutils literal notranslate"><span class="pre">return_value</span></code></a>.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span><span class="w"> </span><span class="nf">some_function</span><span class="p">():</span>
<span class="gp">... </span> <span class="n">instance</span> <span class="o">=</span> <span class="n">module</span><span class="o">.</span><span class="n">Foo</span><span class="p">()</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">instance</span><span class="o">.</span><span class="n">method</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s1">&#39;module.Foo&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">mock</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">instance</span> <span class="o">=</span> <span class="n">mock</span><span class="o">.</span><span class="n">return_value</span>
<span class="gp">... </span> <span class="n">instance</span><span class="o">.</span><span class="n">method</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="s1">&#39;the result&#39;</span>
<span class="gp">... </span> <span class="n">result</span> <span class="o">=</span> <span class="n">some_function</span><span class="p">()</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">result</span> <span class="o">==</span> <span class="s1">&#39;the result&#39;</span>
</pre></div>
</div>
</section>
<section id="naming-your-mocks">
<h3>Naming your mocks<a class="headerlink" href="#naming-your-mocks" title="Link to this heading"></a></h3>
<p>It can be useful to give your mocks a name. The name is shown in the repr of
the mock and can be helpful when the mock appears in test failure messages. The
name is also propagated to attributes or methods of the mock:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s1">&#39;foo&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span>
<span class="go">&lt;MagicMock name=&#39;foo&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">method</span>
<span class="go">&lt;MagicMock name=&#39;foo.method&#39; id=&#39;...&#39;&gt;</span>
</pre></div>
</div>
</section>
<section id="tracking-all-calls">
<h3>Tracking all Calls<a class="headerlink" href="#tracking-all-calls" title="Link to this heading"></a></h3>
<p>Often you want to track more than a single call to a method. The
<a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate"><span class="pre">mock_calls</span></code></a> attribute records all calls
to child attributes of the mock - and also to their children.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">method</span><span class="p">()</span>
<span class="go">&lt;MagicMock name=&#39;mock.method()&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">attribute</span><span class="o">.</span><span class="n">method</span><span class="p">(</span><span class="mi">10</span><span class="p">,</span> <span class="n">x</span><span class="o">=</span><span class="mi">53</span><span class="p">)</span>
<span class="go">&lt;MagicMock name=&#39;mock.attribute.method()&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">mock_calls</span>
<span class="go">[call.method(), call.attribute.method(10, x=53)]</span>
</pre></div>
</div>
<p>If you make an assertion about <code class="docutils literal notranslate"><span class="pre">mock_calls</span></code> and any unexpected methods
have been called, then the assertion will fail. This is useful because as well
as asserting that the calls you expected have been made, you are also checking
that they were made in the right order and with no additional calls:</p>
<p>You use the <a class="reference internal" href="unittest.mock.html#unittest.mock.call" title="unittest.mock.call"><code class="xref py py-data docutils literal notranslate"><span class="pre">call</span></code></a> object to construct lists for comparing with
<code class="docutils literal notranslate"><span class="pre">mock_calls</span></code>:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">expected</span> <span class="o">=</span> <span class="p">[</span><span class="n">call</span><span class="o">.</span><span class="n">method</span><span class="p">(),</span> <span class="n">call</span><span class="o">.</span><span class="n">attribute</span><span class="o">.</span><span class="n">method</span><span class="p">(</span><span class="mi">10</span><span class="p">,</span> <span class="n">x</span><span class="o">=</span><span class="mi">53</span><span class="p">)]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">mock_calls</span> <span class="o">==</span> <span class="n">expected</span>
<span class="go">True</span>
</pre></div>
</div>
<p>However, parameters to calls that return mocks are not recorded, which means it is not
possible to track nested calls where the parameters used to create ancestors are important:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">factory</span><span class="p">(</span><span class="n">important</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span><span class="o">.</span><span class="n">deliver</span><span class="p">()</span>
<span class="go">&lt;Mock name=&#39;mock.factory().deliver()&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">mock_calls</span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span> <span class="o">==</span> <span class="n">call</span><span class="o">.</span><span class="n">factory</span><span class="p">(</span><span class="n">important</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span><span class="o">.</span><span class="n">deliver</span><span class="p">()</span>
<span class="go">True</span>
</pre></div>
</div>
</section>
<section id="setting-return-values-and-attributes">
<h3>Setting Return Values and Attributes<a class="headerlink" href="#setting-return-values-and-attributes" title="Link to this heading"></a></h3>
<p>Setting the return values on a mock object is trivially easy:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">()</span>
<span class="go">3</span>
</pre></div>
</div>
<p>Of course you can do the same for methods on the mock:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">method</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">method</span><span class="p">()</span>
<span class="go">3</span>
</pre></div>
</div>
<p>The return value can also be set in the constructor:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">(</span><span class="n">return_value</span><span class="o">=</span><span class="mi">3</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">()</span>
<span class="go">3</span>
</pre></div>
</div>
<p>If you need an attribute setting on your mock, just do it:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">x</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">x</span>
<span class="go">3</span>
</pre></div>
</div>
<p>Sometimes you want to mock up a more complex situation, like for example
<code class="docutils literal notranslate"><span class="pre">mock.connection.cursor().execute(&quot;SELECT</span> <span class="pre">1&quot;)</span></code>. If we wanted this call to
return a list, then we have to configure the result of the nested call.</p>
<p>We can use <a class="reference internal" href="unittest.mock.html#unittest.mock.call" title="unittest.mock.call"><code class="xref py py-data docutils literal notranslate"><span class="pre">call</span></code></a> to construct the set of calls in a “chained call” like
this for easy assertion afterwards:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">cursor</span> <span class="o">=</span> <span class="n">mock</span><span class="o">.</span><span class="n">connection</span><span class="o">.</span><span class="n">cursor</span><span class="o">.</span><span class="n">return_value</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">cursor</span><span class="o">.</span><span class="n">execute</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="p">[</span><span class="s1">&#39;foo&#39;</span><span class="p">]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">connection</span><span class="o">.</span><span class="n">cursor</span><span class="p">()</span><span class="o">.</span><span class="n">execute</span><span class="p">(</span><span class="s2">&quot;SELECT 1&quot;</span><span class="p">)</span>
<span class="go">[&#39;foo&#39;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">expected</span> <span class="o">=</span> <span class="n">call</span><span class="o">.</span><span class="n">connection</span><span class="o">.</span><span class="n">cursor</span><span class="p">()</span><span class="o">.</span><span class="n">execute</span><span class="p">(</span><span class="s2">&quot;SELECT 1&quot;</span><span class="p">)</span><span class="o">.</span><span class="n">call_list</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">mock_calls</span>
<span class="go">[call.connection.cursor(), call.connection.cursor().execute(&#39;SELECT 1&#39;)]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">mock_calls</span> <span class="o">==</span> <span class="n">expected</span>
<span class="go">True</span>
</pre></div>
</div>
<p>It is the call to <code class="docutils literal notranslate"><span class="pre">.call_list()</span></code> that turns our call object into a list of
calls representing the chained calls.</p>
</section>
<section id="raising-exceptions-with-mocks">
<h3>Raising exceptions with mocks<a class="headerlink" href="#raising-exceptions-with-mocks" title="Link to this heading"></a></h3>
<p>A useful attribute is <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate"><span class="pre">side_effect</span></code></a>. If you set this to an
exception class or instance then the exception will be raised when the mock
is called.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">(</span><span class="n">side_effect</span><span class="o">=</span><span class="ne">Exception</span><span class="p">(</span><span class="s1">&#39;Boom!&#39;</span><span class="p">))</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">()</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="w"> </span><span class="c">...</span>
<span class="gr">Exception</span>: <span class="n">Boom!</span>
</pre></div>
</div>
</section>
<section id="side-effect-functions-and-iterables">
<h3>Side effect functions and iterables<a class="headerlink" href="#side-effect-functions-and-iterables" title="Link to this heading"></a></h3>
<p><code class="docutils literal notranslate"><span class="pre">side_effect</span></code> can also be set to a function or an iterable. The use case for
<code class="docutils literal notranslate"><span class="pre">side_effect</span></code> as an iterable is where your mock is going to be called several
times, and you want each call to return a different value. When you set
<code class="docutils literal notranslate"><span class="pre">side_effect</span></code> to an iterable every call to the mock returns the next value
from the iterable:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">(</span><span class="n">side_effect</span><span class="o">=</span><span class="p">[</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">])</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">()</span>
<span class="go">4</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">()</span>
<span class="go">5</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">()</span>
<span class="go">6</span>
</pre></div>
</div>
<p>For more advanced use cases, like dynamically varying the return values
depending on what the mock is called with, <code class="docutils literal notranslate"><span class="pre">side_effect</span></code> can be a function.
The function will be called with the same arguments as the mock. Whatever the
function returns is what the call returns:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">vals</span> <span class="o">=</span> <span class="p">{(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">):</span> <span class="mi">1</span><span class="p">,</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">):</span> <span class="mi">2</span><span class="p">}</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">def</span><span class="w"> </span><span class="nf">side_effect</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">vals</span><span class="p">[</span><span class="n">args</span><span class="p">]</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">(</span><span class="n">side_effect</span><span class="o">=</span><span class="n">side_effect</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>
<span class="go">1</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<span class="go">2</span>
</pre></div>
</div>
</section>
<section id="mocking-asynchronous-iterators">
<h3>Mocking asynchronous iterators<a class="headerlink" href="#mocking-asynchronous-iterators" title="Link to this heading"></a></h3>
<p>Since Python 3.8, <code class="docutils literal notranslate"><span class="pre">AsyncMock</span></code> and <code class="docutils literal notranslate"><span class="pre">MagicMock</span></code> have support to mock
<a class="reference internal" href="../reference/datamodel.html#async-iterators"><span class="std std-ref">Asynchronous Iterators</span></a> through <code class="docutils literal notranslate"><span class="pre">__aiter__</span></code>. The <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.return_value" title="unittest.mock.Mock.return_value"><code class="xref py py-attr docutils literal notranslate"><span class="pre">return_value</span></code></a>
attribute of <code class="docutils literal notranslate"><span class="pre">__aiter__</span></code> can be used to set the return values to be used for
iteration.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">()</span> <span class="c1"># AsyncMock also works here</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="fm">__aiter__</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">main</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">return</span> <span class="p">[</span><span class="n">i</span> <span class="k">async</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="n">mock</span><span class="p">]</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
<span class="go">[1, 2, 3]</span>
</pre></div>
</div>
</section>
<section id="mocking-asynchronous-context-manager">
<h3>Mocking asynchronous context manager<a class="headerlink" href="#mocking-asynchronous-context-manager" title="Link to this heading"></a></h3>
<p>Since Python 3.8, <code class="docutils literal notranslate"><span class="pre">AsyncMock</span></code> and <code class="docutils literal notranslate"><span class="pre">MagicMock</span></code> have support to mock
<a class="reference internal" href="../reference/datamodel.html#async-context-managers"><span class="std std-ref">Asynchronous Context Managers</span></a> through <code class="docutils literal notranslate"><span class="pre">__aenter__</span></code> and <code class="docutils literal notranslate"><span class="pre">__aexit__</span></code>.
By default, <code class="docutils literal notranslate"><span class="pre">__aenter__</span></code> and <code class="docutils literal notranslate"><span class="pre">__aexit__</span></code> are <code class="docutils literal notranslate"><span class="pre">AsyncMock</span></code> instances that
return an async function.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">AsyncContextManager</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="fm">__aenter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span>
<span class="gp">... </span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="fm">__aexit__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">exc_type</span><span class="p">,</span> <span class="n">exc</span><span class="p">,</span> <span class="n">tb</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">pass</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_instance</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">(</span><span class="n">AsyncContextManager</span><span class="p">())</span> <span class="c1"># AsyncMock also works here</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">main</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">async</span> <span class="k">with</span> <span class="n">mock_instance</span> <span class="k">as</span> <span class="n">result</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">pass</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_instance</span><span class="o">.</span><span class="fm">__aenter__</span><span class="o">.</span><span class="n">assert_awaited_once</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_instance</span><span class="o">.</span><span class="fm">__aexit__</span><span class="o">.</span><span class="n">assert_awaited_once</span><span class="p">()</span>
</pre></div>
</div>
</section>
<section id="creating-a-mock-from-an-existing-object">
<h3>Creating a Mock from an Existing Object<a class="headerlink" href="#creating-a-mock-from-an-existing-object" title="Link to this heading"></a></h3>
<p>One problem with over use of mocking is that it couples your tests to the
implementation of your mocks rather than your real code. Suppose you have a
class that implements <code class="docutils literal notranslate"><span class="pre">some_method</span></code>. In a test for another class, you
provide a mock of this object that <em>also</em> provides <code class="docutils literal notranslate"><span class="pre">some_method</span></code>. If later
you refactor the first class, so that it no longer has <code class="docutils literal notranslate"><span class="pre">some_method</span></code> - then
your tests will continue to pass even though your code is now broken!</p>
<p><a class="reference internal" href="unittest.mock.html#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate"><span class="pre">Mock</span></code></a> allows you to provide an object as a specification for the mock,
using the <em>spec</em> keyword argument. Accessing methods / attributes on the
mock that don’t exist on your specification object will immediately raise an
attribute error. If you change the implementation of your specification, then
tests that use that class will start failing immediately without you having to
instantiate the class in those tests.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">(</span><span class="n">spec</span><span class="o">=</span><span class="n">SomeClass</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">old_method</span><span class="p">()</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="w"> </span><span class="c">...</span>
<span class="gr">AttributeError</span>: <span class="n">Mock object has no attribute &#39;old_method&#39;. Did you mean: &#39;class_method&#39;?</span>
</pre></div>
</div>
<p>Using a specification also enables a smarter matching of calls made to the
mock, regardless of whether some parameters were passed as positional or
named arguments:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span><span class="w"> </span><span class="nf">f</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">,</span> <span class="n">c</span><span class="p">):</span> <span class="k">pass</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">(</span><span class="n">spec</span><span class="o">=</span><span class="n">f</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<span class="go">&lt;Mock name=&#39;mock()&#39; id=&#39;140161580456576&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">(</span><span class="n">a</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">b</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">c</span><span class="o">=</span><span class="mi">3</span><span class="p">)</span>
</pre></div>
</div>
<p>If you want this smarter matching to also work with method calls on the mock,
you can use <a class="reference internal" href="unittest.mock.html#auto-speccing"><span class="std std-ref">auto-speccing</span></a>.</p>
<p>If you want a stronger form of specification that prevents the setting
of arbitrary attributes as well as the getting of them then you can use
<em>spec_set</em> instead of <em>spec</em>.</p>
</section>
<section id="using-side-effect-to-return-per-file-content">
<h3>Using side_effect to return per file content<a class="headerlink" href="#using-side-effect-to-return-per-file-content" title="Link to this heading"></a></h3>
<p><a class="reference internal" href="unittest.mock.html#unittest.mock.mock_open" title="unittest.mock.mock_open"><code class="xref py py-func docutils literal notranslate"><span class="pre">mock_open()</span></code></a> is used to patch <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> method. <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate"><span class="pre">side_effect</span></code></a>
can be used to return a new Mock object per call. This can be used to return different
contents per file stored in a dictionary:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">DEFAULT</span> <span class="o">=</span> <span class="s2">&quot;default&quot;</span>
<span class="n">data_dict</span> <span class="o">=</span> <span class="p">{</span><span class="s2">&quot;file1&quot;</span><span class="p">:</span> <span class="s2">&quot;data1&quot;</span><span class="p">,</span>
<span class="s2">&quot;file2&quot;</span><span class="p">:</span> <span class="s2">&quot;data2&quot;</span><span class="p">}</span>
<span class="k">def</span><span class="w"> </span><span class="nf">open_side_effect</span><span class="p">(</span><span class="n">name</span><span class="p">):</span>
<span class="k">return</span> <span class="n">mock_open</span><span class="p">(</span><span class="n">read_data</span><span class="o">=</span><span class="n">data_dict</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">DEFAULT</span><span class="p">))()</span>
<span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s2">&quot;builtins.open&quot;</span><span class="p">,</span> <span class="n">side_effect</span><span class="o">=</span><span class="n">open_side_effect</span><span class="p">):</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s2">&quot;file1&quot;</span><span class="p">)</span> <span class="k">as</span> <span class="n">file1</span><span class="p">:</span>
<span class="k">assert</span> <span class="n">file1</span><span class="o">.</span><span class="n">read</span><span class="p">()</span> <span class="o">==</span> <span class="s2">&quot;data1&quot;</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s2">&quot;file2&quot;</span><span class="p">)</span> <span class="k">as</span> <span class="n">file2</span><span class="p">:</span>
<span class="k">assert</span> <span class="n">file2</span><span class="o">.</span><span class="n">read</span><span class="p">()</span> <span class="o">==</span> <span class="s2">&quot;data2&quot;</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s2">&quot;file3&quot;</span><span class="p">)</span> <span class="k">as</span> <span class="n">file2</span><span class="p">:</span>
<span class="k">assert</span> <span class="n">file2</span><span class="o">.</span><span class="n">read</span><span class="p">()</span> <span class="o">==</span> <span class="s2">&quot;default&quot;</span>
</pre></div>
</div>
</section>
</section>
<section id="patch-decorators">
<h2>Patch Decorators<a class="headerlink" href="#patch-decorators" title="Link to this heading"></a></h2>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>With <a class="reference internal" href="unittest.mock.html#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch()</span></code></a> it matters that you patch objects in the namespace where
they are looked up. This is normally straightforward, but for a quick guide
read <a class="reference internal" href="unittest.mock.html#where-to-patch"><span class="std std-ref">where to patch</span></a>.</p>
</div>
<p>A common need in tests is to patch a class attribute or a module attribute,
for example patching a builtin or patching a class in a module to test that it
is instantiated. Modules and classes are effectively global, so patching on
them has to be undone after the test or the patch will persist into other
tests and cause hard to diagnose problems.</p>
<p>mock provides three convenient decorators for this: <a class="reference internal" href="unittest.mock.html#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch()</span></code></a>, <a class="reference internal" href="unittest.mock.html#unittest.mock.patch.object" title="unittest.mock.patch.object"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch.object()</span></code></a> and
<a class="reference internal" href="unittest.mock.html#unittest.mock.patch.dict" title="unittest.mock.patch.dict"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch.dict()</span></code></a>. <code class="docutils literal notranslate"><span class="pre">patch</span></code> takes a single string, of the form
<code class="docutils literal notranslate"><span class="pre">package.module.Class.attribute</span></code> to specify the attribute you are patching. It
also optionally takes a value that you want the attribute (or class or
whatever) to be replaced with. ‘patch.object’ takes an object and the name of
the attribute you would like patched, plus optionally the value to patch it
with.</p>
<p><code class="docutils literal notranslate"><span class="pre">patch.object</span></code>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">original</span> <span class="o">=</span> <span class="n">SomeClass</span><span class="o">.</span><span class="n">attribute</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nd">@patch</span><span class="o">.</span><span class="n">object</span><span class="p">(</span><span class="n">SomeClass</span><span class="p">,</span> <span class="s1">&#39;attribute&#39;</span><span class="p">,</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">attribute</span><span class="p">)</span>
<span class="gp">... </span><span class="k">def</span><span class="w"> </span><span class="nf">test</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">SomeClass</span><span class="o">.</span><span class="n">attribute</span> <span class="o">==</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">attribute</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">test</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">assert</span> <span class="n">SomeClass</span><span class="o">.</span><span class="n">attribute</span> <span class="o">==</span> <span class="n">original</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nd">@patch</span><span class="p">(</span><span class="s1">&#39;package.module.attribute&#39;</span><span class="p">,</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">attribute</span><span class="p">)</span>
<span class="gp">... </span><span class="k">def</span><span class="w"> </span><span class="nf">test</span><span class="p">():</span>
<span class="gp">... </span> <span class="kn">from</span><span class="w"> </span><span class="nn">package.module</span><span class="w"> </span><span class="kn">import</span> <span class="n">attribute</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">attribute</span> <span class="ow">is</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">attribute</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">test</span><span class="p">()</span>
</pre></div>
</div>
<p>If you are patching a module (including <a class="reference internal" href="builtins.html#module-builtins" title="builtins: The module that provides the built-in namespace."><code class="xref py py-mod docutils literal notranslate"><span class="pre">builtins</span></code></a>) then use <a class="reference internal" href="unittest.mock.html#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch()</span></code></a>
instead of <a class="reference internal" href="unittest.mock.html#unittest.mock.patch.object" title="unittest.mock.patch.object"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch.object()</span></code></a>:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">(</span><span class="n">return_value</span><span class="o">=</span><span class="n">sentinel</span><span class="o">.</span><span class="n">file_handle</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s1">&#39;builtins.open&#39;</span><span class="p">,</span> <span class="n">mock</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">handle</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="s1">&#39;filename&#39;</span><span class="p">,</span> <span class="s1">&#39;r&#39;</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">(</span><span class="s1">&#39;filename&#39;</span><span class="p">,</span> <span class="s1">&#39;r&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">assert</span> <span class="n">handle</span> <span class="o">==</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">file_handle</span><span class="p">,</span> <span class="s2">&quot;incorrect file handle returned&quot;</span>
</pre></div>
</div>
<p>The module name can be ‘dotted’, in the form <code class="docutils literal notranslate"><span class="pre">package.module</span></code> if needed:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="nd">@patch</span><span class="p">(</span><span class="s1">&#39;package.module.ClassName.attribute&#39;</span><span class="p">,</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">attribute</span><span class="p">)</span>
<span class="gp">... </span><span class="k">def</span><span class="w"> </span><span class="nf">test</span><span class="p">():</span>
<span class="gp">... </span> <span class="kn">from</span><span class="w"> </span><span class="nn">package.module</span><span class="w"> </span><span class="kn">import</span> <span class="n">ClassName</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">ClassName</span><span class="o">.</span><span class="n">attribute</span> <span class="o">==</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">attribute</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">test</span><span class="p">()</span>
</pre></div>
</div>
<p>A nice pattern is to actually decorate test methods themselves:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">MyTest</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>
<span class="gp">... </span> <span class="nd">@patch</span><span class="o">.</span><span class="n">object</span><span class="p">(</span><span class="n">SomeClass</span><span class="p">,</span> <span class="s1">&#39;attribute&#39;</span><span class="p">,</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">attribute</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">test_something</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">assertEqual</span><span class="p">(</span><span class="n">SomeClass</span><span class="o">.</span><span class="n">attribute</span><span class="p">,</span> <span class="n">sentinel</span><span class="o">.</span><span class="n">attribute</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">original</span> <span class="o">=</span> <span class="n">SomeClass</span><span class="o">.</span><span class="n">attribute</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">MyTest</span><span class="p">(</span><span class="s1">&#39;test_something&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">test_something</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">assert</span> <span class="n">SomeClass</span><span class="o">.</span><span class="n">attribute</span> <span class="o">==</span> <span class="n">original</span>
</pre></div>
</div>
<p>If you want to patch with a Mock, you can use <a class="reference internal" href="unittest.mock.html#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch()</span></code></a> with only one argument
(or <a class="reference internal" href="unittest.mock.html#unittest.mock.patch.object" title="unittest.mock.patch.object"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch.object()</span></code></a> with two arguments). The mock will be created for you and
passed into the test function / method:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">MyTest</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>
<span class="gp">... </span> <span class="nd">@patch</span><span class="o">.</span><span class="n">object</span><span class="p">(</span><span class="n">SomeClass</span><span class="p">,</span> <span class="s1">&#39;static_method&#39;</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">test_something</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">mock_method</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">SomeClass</span><span class="o">.</span><span class="n">static_method</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">mock_method</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">MyTest</span><span class="p">(</span><span class="s1">&#39;test_something&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">test_something</span><span class="p">()</span>
</pre></div>
</div>
<p>You can stack up multiple patch decorators using this pattern:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">MyTest</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>
<span class="gp">... </span> <span class="nd">@patch</span><span class="p">(</span><span class="s1">&#39;package.module.ClassName1&#39;</span><span class="p">)</span>
<span class="gp">... </span> <span class="nd">@patch</span><span class="p">(</span><span class="s1">&#39;package.module.ClassName2&#39;</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">test_something</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">MockClass2</span><span class="p">,</span> <span class="n">MockClass1</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">assertIs</span><span class="p">(</span><span class="n">package</span><span class="o">.</span><span class="n">module</span><span class="o">.</span><span class="n">ClassName1</span><span class="p">,</span> <span class="n">MockClass1</span><span class="p">)</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">assertIs</span><span class="p">(</span><span class="n">package</span><span class="o">.</span><span class="n">module</span><span class="o">.</span><span class="n">ClassName2</span><span class="p">,</span> <span class="n">MockClass2</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">MyTest</span><span class="p">(</span><span class="s1">&#39;test_something&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">test_something</span><span class="p">()</span>
</pre></div>
</div>
<p>When you nest patch decorators the mocks are passed in to the decorated
function in the same order they applied (the normal <em>Python</em> order that
decorators are applied). This means from the bottom up, so in the example
above the mock for <code class="docutils literal notranslate"><span class="pre">test_module.ClassName2</span></code> is passed in first.</p>
<p>There is also <a class="reference internal" href="unittest.mock.html#unittest.mock.patch.dict" title="unittest.mock.patch.dict"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch.dict()</span></code></a> for setting values in a dictionary just
during a scope and restoring the dictionary to its original state when the test
ends:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">foo</span> <span class="o">=</span> <span class="p">{</span><span class="s1">&#39;key&#39;</span><span class="p">:</span> <span class="s1">&#39;value&#39;</span><span class="p">}</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">original</span> <span class="o">=</span> <span class="n">foo</span><span class="o">.</span><span class="n">copy</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">patch</span><span class="o">.</span><span class="n">dict</span><span class="p">(</span><span class="n">foo</span><span class="p">,</span> <span class="p">{</span><span class="s1">&#39;newkey&#39;</span><span class="p">:</span> <span class="s1">&#39;newvalue&#39;</span><span class="p">},</span> <span class="n">clear</span><span class="o">=</span><span class="kc">True</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">foo</span> <span class="o">==</span> <span class="p">{</span><span class="s1">&#39;newkey&#39;</span><span class="p">:</span> <span class="s1">&#39;newvalue&#39;</span><span class="p">}</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">assert</span> <span class="n">foo</span> <span class="o">==</span> <span class="n">original</span>
</pre></div>
</div>
<p><code class="docutils literal notranslate"><span class="pre">patch</span></code>, <code class="docutils literal notranslate"><span class="pre">patch.object</span></code> and <code class="docutils literal notranslate"><span class="pre">patch.dict</span></code> can all be used as context managers.</p>
<p>Where you use <a class="reference internal" href="unittest.mock.html#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch()</span></code></a> to create a mock for you, you can get a reference to the
mock using the “as” form of the with statement:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">ProductionClass</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">method</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">pass</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">patch</span><span class="o">.</span><span class="n">object</span><span class="p">(</span><span class="n">ProductionClass</span><span class="p">,</span> <span class="s1">&#39;method&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">mock_method</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">mock_method</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="kc">None</span>
<span class="gp">... </span> <span class="n">real</span> <span class="o">=</span> <span class="n">ProductionClass</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">real</span><span class="o">.</span><span class="n">method</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_method</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
</pre></div>
</div>
<p>As an alternative <code class="docutils literal notranslate"><span class="pre">patch</span></code>, <code class="docutils literal notranslate"><span class="pre">patch.object</span></code> and <code class="docutils literal notranslate"><span class="pre">patch.dict</span></code> can be used as
class decorators. When used in this way it is the same as applying the
decorator individually to every method whose name starts with “test”.</p>
</section>
<section id="further-examples">
<span id="id1"></span><h2>Further Examples<a class="headerlink" href="#further-examples" title="Link to this heading"></a></h2>
<p>Here are some more examples for some slightly more advanced scenarios.</p>
<section id="mocking-chained-calls">
<h3>Mocking chained calls<a class="headerlink" href="#mocking-chained-calls" title="Link to this heading"></a></h3>
<p>Mocking chained calls is actually straightforward with mock once you
understand the <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.return_value" title="unittest.mock.Mock.return_value"><code class="xref py py-attr docutils literal notranslate"><span class="pre">return_value</span></code></a> attribute. When a mock is called for
the first time, or you fetch its <code class="docutils literal notranslate"><span class="pre">return_value</span></code> before it has been called, a
new <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate"><span class="pre">Mock</span></code></a> is created.</p>
<p>This means that you can see how the object returned from a call to a mocked
object has been used by interrogating the <code class="docutils literal notranslate"><span class="pre">return_value</span></code> mock:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">()</span><span class="o">.</span><span class="n">foo</span><span class="p">(</span><span class="n">a</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">b</span><span class="o">=</span><span class="mi">3</span><span class="p">)</span>
<span class="go">&lt;Mock name=&#39;mock().foo()&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">return_value</span><span class="o">.</span><span class="n">foo</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">(</span><span class="n">a</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">b</span><span class="o">=</span><span class="mi">3</span><span class="p">)</span>
</pre></div>
</div>
<p>From here it is a simple step to configure and then make assertions about
chained calls. Of course another alternative is writing your code in a more
testable way in the first place…</p>
<p>So, suppose we have some code that looks a little bit like this:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">Something</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">backend</span> <span class="o">=</span> <span class="n">BackendProvider</span><span class="p">()</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">method</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">response</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">backend</span><span class="o">.</span><span class="n">get_endpoint</span><span class="p">(</span><span class="s1">&#39;foobar&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">create_call</span><span class="p">(</span><span class="s1">&#39;spam&#39;</span><span class="p">,</span> <span class="s1">&#39;eggs&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">start_call</span><span class="p">()</span>
<span class="gp">... </span> <span class="c1"># more code</span>
</pre></div>
</div>
<p>Assuming that <code class="docutils literal notranslate"><span class="pre">BackendProvider</span></code> is already well tested, how do we test
<code class="docutils literal notranslate"><span class="pre">method()</span></code>? Specifically, we want to test that the code section <code class="docutils literal notranslate"><span class="pre">#</span> <span class="pre">more</span>
<span class="pre">code</span></code> uses the response object in the correct way.</p>
<p>As this chain of calls is made from an instance attribute we can monkey patch
the <code class="docutils literal notranslate"><span class="pre">backend</span></code> attribute on a <code class="docutils literal notranslate"><span class="pre">Something</span></code> instance. In this particular case
we are only interested in the return value from the final call to
<code class="docutils literal notranslate"><span class="pre">start_call</span></code> so we don’t have much configuration to do. Let’s assume the
object it returns is ‘file-like’, so we’ll ensure that our response object
uses the builtin <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> as its <code class="docutils literal notranslate"><span class="pre">spec</span></code>.</p>
<p>To do this we create a mock instance as our mock backend and create a mock
response object for it. To set the response as the return value for that final
<code class="docutils literal notranslate"><span class="pre">start_call</span></code> we could do this:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">mock_backend</span><span class="o">.</span><span class="n">get_endpoint</span><span class="o">.</span><span class="n">return_value</span><span class="o">.</span><span class="n">create_call</span><span class="o">.</span><span class="n">return_value</span><span class="o">.</span><span class="n">start_call</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="n">mock_response</span>
</pre></div>
</div>
<p>We can do that in a slightly nicer way using the <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.configure_mock" title="unittest.mock.Mock.configure_mock"><code class="xref py py-meth docutils literal notranslate"><span class="pre">configure_mock()</span></code></a>
method to directly set the return value for us:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">something</span> <span class="o">=</span> <span class="n">Something</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_response</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">(</span><span class="n">spec</span><span class="o">=</span><span class="nb">open</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_backend</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">config</span> <span class="o">=</span> <span class="p">{</span><span class="s1">&#39;get_endpoint.return_value.create_call.return_value.start_call.return_value&#39;</span><span class="p">:</span> <span class="n">mock_response</span><span class="p">}</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_backend</span><span class="o">.</span><span class="n">configure_mock</span><span class="p">(</span><span class="o">**</span><span class="n">config</span><span class="p">)</span>
</pre></div>
</div>
<p>With these we monkey patch the “mock backend” in place and can make the real
call:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">something</span><span class="o">.</span><span class="n">backend</span> <span class="o">=</span> <span class="n">mock_backend</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">something</span><span class="o">.</span><span class="n">method</span><span class="p">()</span>
</pre></div>
</div>
<p>Using <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate"><span class="pre">mock_calls</span></code></a> we can check the chained call with a single
assert. A chained call is several calls in one line of code, so there will be
several entries in <code class="docutils literal notranslate"><span class="pre">mock_calls</span></code>. We can use <a class="reference internal" href="unittest.mock.html#unittest.mock.call.call_list" title="unittest.mock.call.call_list"><code class="xref py py-meth docutils literal notranslate"><span class="pre">call.call_list()</span></code></a> to create
this list of calls for us:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">chained</span> <span class="o">=</span> <span class="n">call</span><span class="o">.</span><span class="n">get_endpoint</span><span class="p">(</span><span class="s1">&#39;foobar&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">create_call</span><span class="p">(</span><span class="s1">&#39;spam&#39;</span><span class="p">,</span> <span class="s1">&#39;eggs&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">start_call</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">call_list</span> <span class="o">=</span> <span class="n">chained</span><span class="o">.</span><span class="n">call_list</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">assert</span> <span class="n">mock_backend</span><span class="o">.</span><span class="n">mock_calls</span> <span class="o">==</span> <span class="n">call_list</span>
</pre></div>
</div>
</section>
<section id="partial-mocking">
<h3>Partial mocking<a class="headerlink" href="#partial-mocking" title="Link to this heading"></a></h3>
<p>In some tests I wanted to mock out a call to <a class="reference internal" href="datetime.html#datetime.date.today" title="datetime.date.today"><code class="xref py py-meth docutils literal notranslate"><span class="pre">datetime.date.today()</span></code></a>
to return a known date, but I didn’t want to prevent the code under test from
creating new date objects. Unfortunately <a class="reference internal" href="datetime.html#datetime.date" title="datetime.date"><code class="xref py py-class docutils literal notranslate"><span class="pre">datetime.date</span></code></a> is written in C, and
so I couldn’t just monkey-patch out the static <a class="reference internal" href="datetime.html#datetime.date.today" title="datetime.date.today"><code class="xref py py-meth docutils literal notranslate"><span class="pre">datetime.date.today()</span></code></a> method.</p>
<p>I found a simple way of doing this that involved effectively wrapping the date
class with a mock, but passing through calls to the constructor to the real
class (and returning real instances).</p>
<p>The <a class="reference internal" href="unittest.mock.html#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch</span> <span class="pre">decorator</span></code></a> is used here to
mock out the <code class="docutils literal notranslate"><span class="pre">date</span></code> class in the module under test. The <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate"><span class="pre">side_effect</span></code></a>
attribute on the mock date class is then set to a lambda function that returns
a real date. When the mock date class is called a real date will be
constructed and returned by <code class="docutils literal notranslate"><span class="pre">side_effect</span></code>.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span><span class="w"> </span><span class="nn">datetime</span><span class="w"> </span><span class="kn">import</span> <span class="n">date</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s1">&#39;mymodule.date&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">mock_date</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">mock_date</span><span class="o">.</span><span class="n">today</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="n">date</span><span class="p">(</span><span class="mi">2010</span><span class="p">,</span> <span class="mi">10</span><span class="p">,</span> <span class="mi">8</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">mock_date</span><span class="o">.</span><span class="n">side_effect</span> <span class="o">=</span> <span class="k">lambda</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kw</span><span class="p">:</span> <span class="n">date</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kw</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">mymodule</span><span class="o">.</span><span class="n">date</span><span class="o">.</span><span class="n">today</span><span class="p">()</span> <span class="o">==</span> <span class="n">date</span><span class="p">(</span><span class="mi">2010</span><span class="p">,</span> <span class="mi">10</span><span class="p">,</span> <span class="mi">8</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">mymodule</span><span class="o">.</span><span class="n">date</span><span class="p">(</span><span class="mi">2009</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">8</span><span class="p">)</span> <span class="o">==</span> <span class="n">date</span><span class="p">(</span><span class="mi">2009</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">8</span><span class="p">)</span>
</pre></div>
</div>
<p>Note that we don’t patch <a class="reference internal" href="datetime.html#datetime.date" title="datetime.date"><code class="xref py py-class docutils literal notranslate"><span class="pre">datetime.date</span></code></a> globally, we patch <code class="docutils literal notranslate"><span class="pre">date</span></code> in the
module that <em>uses</em> it. See <a class="reference internal" href="unittest.mock.html#where-to-patch"><span class="std std-ref">where to patch</span></a>.</p>
<p>When <code class="docutils literal notranslate"><span class="pre">date.today()</span></code> is called a known date is returned, but calls to the
<code class="docutils literal notranslate"><span class="pre">date(...)</span></code> constructor still return normal dates. Without this you can find
yourself having to calculate an expected result using exactly the same
algorithm as the code under test, which is a classic testing anti-pattern.</p>
<p>Calls to the date constructor are recorded in the <code class="docutils literal notranslate"><span class="pre">mock_date</span></code> attributes
(<code class="docutils literal notranslate"><span class="pre">call_count</span></code> and friends) which may also be useful for your tests.</p>
<p>An alternative way of dealing with mocking dates, or other builtin classes,
is discussed in <a class="reference external" href="https://williambert.online/2011/07/how-to-unit-testing-in-django-with-mocking-and-patching/">this blog entry</a>.</p>
</section>
<section id="mocking-a-generator-method">
<h3>Mocking a Generator Method<a class="headerlink" href="#mocking-a-generator-method" title="Link to this heading"></a></h3>
<p>A Python generator is a function or method that uses the <a class="reference internal" href="../reference/simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">yield</span></code></a> statement
to return a series of values when iterated over <a class="footnote-reference brackets" href="#id3" id="id2" role="doc-noteref"><span class="fn-bracket">[</span>1<span class="fn-bracket">]</span></a>.</p>
<p>A generator method / function is called to return the generator object. It is
the generator object that is then iterated over. The protocol method for
iteration is <a class="reference internal" href="stdtypes.html#container.__iter__" title="container.__iter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__iter__()</span></code></a>, so we can
mock this using a <a class="reference internal" href="unittest.mock.html#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate"><span class="pre">MagicMock</span></code></a>.</p>
<p>Here’s an example class with an “iter” method implemented as a generator:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">Foo</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">iter</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]:</span>
<span class="gp">... </span> <span class="k">yield</span> <span class="n">i</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">foo</span> <span class="o">=</span> <span class="n">Foo</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">list</span><span class="p">(</span><span class="n">foo</span><span class="o">.</span><span class="n">iter</span><span class="p">())</span>
<span class="go">[1, 2, 3]</span>
</pre></div>
</div>
<p>How would we mock this class, and in particular its “iter” method?</p>
<p>To configure the values returned from the iteration (implicit in the call to
<a class="reference internal" href="stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate"><span class="pre">list</span></code></a>), we need to configure the object returned by the call to <code class="docutils literal notranslate"><span class="pre">foo.iter()</span></code>.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock_foo</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_foo</span><span class="o">.</span><span class="n">iter</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="nb">iter</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">])</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">list</span><span class="p">(</span><span class="n">mock_foo</span><span class="o">.</span><span class="n">iter</span><span class="p">())</span>
<span class="go">[1, 2, 3]</span>
</pre></div>
</div>
<aside class="footnote-list brackets">
<aside class="footnote brackets" id="id3" role="doc-footnote">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id2">1</a><span class="fn-bracket">]</span></span>
<p>There are also generator expressions and more <a class="reference external" href="http://www.dabeaz.com/coroutines/index.html">advanced uses</a> of generators, but we aren’t
concerned about them here. A very good introduction to generators and how
powerful they are is: <a class="reference external" href="http://www.dabeaz.com/generators/">Generator Tricks for Systems Programmers</a>.</p>
</aside>
</aside>
</section>
<section id="applying-the-same-patch-to-every-test-method">
<h3>Applying the same patch to every test method<a class="headerlink" href="#applying-the-same-patch-to-every-test-method" title="Link to this heading"></a></h3>
<p>If you want several patches in place for multiple test methods the obvious way
is to apply the patch decorators to every method. This can feel like unnecessary
repetition. Instead, you can use <a class="reference internal" href="unittest.mock.html#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch()</span></code></a> (in all its
various forms) as a class decorator. This applies the patches to all test
methods on the class. A test method is identified by methods whose names start
with <code class="docutils literal notranslate"><span class="pre">test</span></code>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="nd">@patch</span><span class="p">(</span><span class="s1">&#39;mymodule.SomeClass&#39;</span><span class="p">)</span>
<span class="gp">... </span><span class="k">class</span><span class="w"> </span><span class="nc">MyTest</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">test_one</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">MockSomeClass</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">assertIs</span><span class="p">(</span><span class="n">mymodule</span><span class="o">.</span><span class="n">SomeClass</span><span class="p">,</span> <span class="n">MockSomeClass</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">test_two</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">MockSomeClass</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">assertIs</span><span class="p">(</span><span class="n">mymodule</span><span class="o">.</span><span class="n">SomeClass</span><span class="p">,</span> <span class="n">MockSomeClass</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">not_a_test</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="s1">&#39;something&#39;</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">MyTest</span><span class="p">(</span><span class="s1">&#39;test_one&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">test_one</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">MyTest</span><span class="p">(</span><span class="s1">&#39;test_two&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">test_two</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">MyTest</span><span class="p">(</span><span class="s1">&#39;test_two&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">not_a_test</span><span class="p">()</span>
<span class="go">&#39;something&#39;</span>
</pre></div>
</div>
<p>An alternative way of managing patches is to use the <a class="reference internal" href="unittest.mock.html#start-and-stop"><span class="std std-ref">patch methods: start and stop</span></a>.
These allow you to move the patching into your <code class="docutils literal notranslate"><span class="pre">setUp</span></code> and <code class="docutils literal notranslate"><span class="pre">tearDown</span></code> methods.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">MyTest</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">setUp</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">patcher</span> <span class="o">=</span> <span class="n">patch</span><span class="p">(</span><span class="s1">&#39;mymodule.foo&#39;</span><span class="p">)</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">mock_foo</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">patcher</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">test_foo</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">assertIs</span><span class="p">(</span><span class="n">mymodule</span><span class="o">.</span><span class="n">foo</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">mock_foo</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">tearDown</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">patcher</span><span class="o">.</span><span class="n">stop</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">MyTest</span><span class="p">(</span><span class="s1">&#39;test_foo&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">run</span><span class="p">()</span>
</pre></div>
</div>
<p>If you use this technique you must ensure that the patching is “undone” by
calling <code class="docutils literal notranslate"><span class="pre">stop</span></code>. This can be fiddlier than you might think, because if an
exception is raised in the setUp then tearDown is not called.
<a class="reference internal" href="unittest.html#unittest.TestCase.addCleanup" title="unittest.TestCase.addCleanup"><code class="xref py py-meth docutils literal notranslate"><span class="pre">unittest.TestCase.addCleanup()</span></code></a> makes this easier:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">MyTest</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">setUp</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">patcher</span> <span class="o">=</span> <span class="n">patch</span><span class="p">(</span><span class="s1">&#39;mymodule.foo&#39;</span><span class="p">)</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">addCleanup</span><span class="p">(</span><span class="n">patcher</span><span class="o">.</span><span class="n">stop</span><span class="p">)</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">mock_foo</span> <span class="o">=</span> <span class="n">patcher</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">test_foo</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">assertIs</span><span class="p">(</span><span class="n">mymodule</span><span class="o">.</span><span class="n">foo</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">mock_foo</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">MyTest</span><span class="p">(</span><span class="s1">&#39;test_foo&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">run</span><span class="p">()</span>
</pre></div>
</div>
</section>
<section id="mocking-unbound-methods">
<h3>Mocking Unbound Methods<a class="headerlink" href="#mocking-unbound-methods" title="Link to this heading"></a></h3>
<p>Whilst writing tests today I needed to patch an <em>unbound method</em> (patching the
method on the class rather than on the instance). I needed self to be passed
in as the first argument because I want to make asserts about which objects
were calling this particular method. The issue is that you can’t patch with a
mock for this, because if you replace an unbound method with a mock it doesn’t
become a bound method when fetched from the instance, and so it doesn’t get
self passed in. The workaround is to patch the unbound method with a real
function instead. The <a class="reference internal" href="unittest.mock.html#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch()</span></code></a> decorator makes it so simple to
patch out methods with a mock that having to create a real function becomes a
nuisance.</p>
<p>If you pass <code class="docutils literal notranslate"><span class="pre">autospec=True</span></code> to patch then it does the patching with a
<em>real</em> function object. This function object has the same signature as the one
it is replacing, but delegates to a mock under the hood. You still get your
mock auto-created in exactly the same way as before. What it means though, is
that if you use it to patch out an unbound method on a class the mocked
function will be turned into a bound method if it is fetched from an instance.
It will have <code class="docutils literal notranslate"><span class="pre">self</span></code> passed in as the first argument, which is exactly what I
wanted:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">Foo</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">foo</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">pass</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">patch</span><span class="o">.</span><span class="n">object</span><span class="p">(</span><span class="n">Foo</span><span class="p">,</span> <span class="s1">&#39;foo&#39;</span><span class="p">,</span> <span class="n">autospec</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span> <span class="k">as</span> <span class="n">mock_foo</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">mock_foo</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="s1">&#39;foo&#39;</span>
<span class="gp">... </span> <span class="n">foo</span> <span class="o">=</span> <span class="n">Foo</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">foo</span><span class="o">.</span><span class="n">foo</span><span class="p">()</span>
<span class="gp">...</span>
<span class="go">&#39;foo&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_foo</span><span class="o">.</span><span class="n">assert_called_once_with</span><span class="p">(</span><span class="n">foo</span><span class="p">)</span>
</pre></div>
</div>
<p>If we don’t use <code class="docutils literal notranslate"><span class="pre">autospec=True</span></code> then the unbound method is patched out
with a Mock instance instead, and isn’t called with <code class="docutils literal notranslate"><span class="pre">self</span></code>.</p>
</section>
<section id="checking-multiple-calls-with-mock">
<h3>Checking multiple calls with mock<a class="headerlink" href="#checking-multiple-calls-with-mock" title="Link to this heading"></a></h3>
<p>mock has a nice API for making assertions about how your mock objects are used.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">foo_bar</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="kc">None</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">foo_bar</span><span class="p">(</span><span class="s1">&#39;baz&#39;</span><span class="p">,</span> <span class="n">spam</span><span class="o">=</span><span class="s1">&#39;eggs&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">foo_bar</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">(</span><span class="s1">&#39;baz&#39;</span><span class="p">,</span> <span class="n">spam</span><span class="o">=</span><span class="s1">&#39;eggs&#39;</span><span class="p">)</span>
</pre></div>
</div>
<p>If your mock is only being called once you can use the
<a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.assert_called_once_with" title="unittest.mock.Mock.assert_called_once_with"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assert_called_once_with()</span></code></a> method that also asserts that the
<a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.call_count" title="unittest.mock.Mock.call_count"><code class="xref py py-attr docutils literal notranslate"><span class="pre">call_count</span></code></a> is one.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">foo_bar</span><span class="o">.</span><span class="n">assert_called_once_with</span><span class="p">(</span><span class="s1">&#39;baz&#39;</span><span class="p">,</span> <span class="n">spam</span><span class="o">=</span><span class="s1">&#39;eggs&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">foo_bar</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">foo_bar</span><span class="o">.</span><span class="n">assert_called_once_with</span><span class="p">(</span><span class="s1">&#39;baz&#39;</span><span class="p">,</span> <span class="n">spam</span><span class="o">=</span><span class="s1">&#39;eggs&#39;</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="w"> </span><span class="o">...</span>
<span class="gr">AssertionError</span>: <span class="n">Expected &#39;foo_bar&#39; to be called once. Called 2 times.</span>
<span class="x">Calls: [call(&#39;baz&#39;, spam=&#39;eggs&#39;), call()].</span>
</pre></div>
</div>
<p>Both <code class="docutils literal notranslate"><span class="pre">assert_called_with</span></code> and <code class="docutils literal notranslate"><span class="pre">assert_called_once_with</span></code> make assertions about
the <em>most recent</em> call. If your mock is going to be called several times, and
you want to make assertions about <em>all</em> those calls you can use
<a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.call_args_list" title="unittest.mock.Mock.call_args_list"><code class="xref py py-attr docutils literal notranslate"><span class="pre">call_args_list</span></code></a>:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">(</span><span class="n">return_value</span><span class="o">=</span><span class="kc">None</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">(</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">call_args_list</span>
<span class="go">[call(1, 2, 3), call(4, 5, 6), call()]</span>
</pre></div>
</div>
<p>The <a class="reference internal" href="unittest.mock.html#unittest.mock.call" title="unittest.mock.call"><code class="xref py py-data docutils literal notranslate"><span class="pre">call</span></code></a> helper makes it easy to make assertions about these calls. You
can build up a list of expected calls and compare it to <code class="docutils literal notranslate"><span class="pre">call_args_list</span></code>. This
looks remarkably similar to the repr of the <code class="docutils literal notranslate"><span class="pre">call_args_list</span></code>:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">expected</span> <span class="o">=</span> <span class="p">[</span><span class="n">call</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">),</span> <span class="n">call</span><span class="p">(</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">),</span> <span class="n">call</span><span class="p">()]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">call_args_list</span> <span class="o">==</span> <span class="n">expected</span>
<span class="go">True</span>
</pre></div>
</div>
</section>
<section id="coping-with-mutable-arguments">
<h3>Coping with mutable arguments<a class="headerlink" href="#coping-with-mutable-arguments" title="Link to this heading"></a></h3>
<p>Another situation is rare, but can bite you, is when your mock is called with
mutable arguments. <code class="docutils literal notranslate"><span class="pre">call_args</span></code> and <code class="docutils literal notranslate"><span class="pre">call_args_list</span></code> store <em>references</em> to the
arguments. If the arguments are mutated by the code under test then you can no
longer make assertions about what the values were when the mock was called.</p>
<p>Here’s some example code that shows the problem. Imagine the following functions
defined in ‘mymodule’:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span><span class="w"> </span><span class="nf">frob</span><span class="p">(</span><span class="n">val</span><span class="p">):</span>
<span class="k">pass</span>
<span class="k">def</span><span class="w"> </span><span class="nf">grob</span><span class="p">(</span><span class="n">val</span><span class="p">):</span>
<span class="s2">&quot;First frob and then clear val&quot;</span>
<span class="n">frob</span><span class="p">(</span><span class="n">val</span><span class="p">)</span>
<span class="n">val</span><span class="o">.</span><span class="n">clear</span><span class="p">()</span>
</pre></div>
</div>
<p>When we try to test that <code class="docutils literal notranslate"><span class="pre">grob</span></code> calls <code class="docutils literal notranslate"><span class="pre">frob</span></code> with the correct argument look
what happens:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s1">&#39;mymodule.frob&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">mock_frob</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">val</span> <span class="o">=</span> <span class="p">{</span><span class="mi">6</span><span class="p">}</span>
<span class="gp">... </span> <span class="n">mymodule</span><span class="o">.</span><span class="n">grob</span><span class="p">(</span><span class="n">val</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">val</span>
<span class="go">set()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_frob</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">({</span><span class="mi">6</span><span class="p">})</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="w"> </span><span class="o">...</span>
<span class="gr">AssertionError</span>: <span class="n">Expected: (({6},), {})</span>
<span class="x">Called with: ((set(),), {})</span>
</pre></div>
</div>
<p>One possibility would be for mock to copy the arguments you pass in. This
could then cause problems if you do assertions that rely on object identity
for equality.</p>
<p>Here’s one solution that uses the <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate"><span class="pre">side_effect</span></code></a>
functionality. If you provide a <code class="docutils literal notranslate"><span class="pre">side_effect</span></code> function for a mock then
<code class="docutils literal notranslate"><span class="pre">side_effect</span></code> will be called with the same args as the mock. This gives us an
opportunity to copy the arguments and store them for later assertions. In this
example I’m using <em>another</em> mock to store the arguments so that I can use the
mock methods for doing the assertion. Again a helper function sets this up for
me.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span><span class="w"> </span><span class="nn">copy</span><span class="w"> </span><span class="kn">import</span> <span class="n">deepcopy</span>
<span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span><span class="w"> </span><span class="nn">unittest.mock</span><span class="w"> </span><span class="kn">import</span> <span class="n">Mock</span><span class="p">,</span> <span class="n">patch</span><span class="p">,</span> <span class="n">DEFAULT</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">def</span><span class="w"> </span><span class="nf">copy_call_args</span><span class="p">(</span><span class="n">mock</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">new_mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">side_effect</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">args</span> <span class="o">=</span> <span class="n">deepcopy</span><span class="p">(</span><span class="n">args</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">kwargs</span> <span class="o">=</span> <span class="n">deepcopy</span><span class="p">(</span><span class="n">kwargs</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">new_mock</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">DEFAULT</span>
<span class="gp">... </span> <span class="n">mock</span><span class="o">.</span><span class="n">side_effect</span> <span class="o">=</span> <span class="n">side_effect</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">new_mock</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s1">&#39;mymodule.frob&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">mock_frob</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">new_mock</span> <span class="o">=</span> <span class="n">copy_call_args</span><span class="p">(</span><span class="n">mock_frob</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">val</span> <span class="o">=</span> <span class="p">{</span><span class="mi">6</span><span class="p">}</span>
<span class="gp">... </span> <span class="n">mymodule</span><span class="o">.</span><span class="n">grob</span><span class="p">(</span><span class="n">val</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">new_mock</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">({</span><span class="mi">6</span><span class="p">})</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">new_mock</span><span class="o">.</span><span class="n">call_args</span>
<span class="go">call({6})</span>
</pre></div>
</div>
<p><code class="docutils literal notranslate"><span class="pre">copy_call_args</span></code> is called with the mock that will be called. It returns a new
mock that we do the assertion on. The <code class="docutils literal notranslate"><span class="pre">side_effect</span></code> function makes a copy of
the args and calls our <code class="docutils literal notranslate"><span class="pre">new_mock</span></code> with the copy.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>If your mock is only going to be used once there is an easier way of
checking arguments at the point they are called. You can simply do the
checking inside a <code class="docutils literal notranslate"><span class="pre">side_effect</span></code> function.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span><span class="w"> </span><span class="nf">side_effect</span><span class="p">(</span><span class="n">arg</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">arg</span> <span class="o">==</span> <span class="p">{</span><span class="mi">6</span><span class="p">}</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">(</span><span class="n">side_effect</span><span class="o">=</span><span class="n">side_effect</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">({</span><span class="mi">6</span><span class="p">})</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">(</span><span class="nb">set</span><span class="p">())</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="w"> </span><span class="o">...</span>
<span class="gr">AssertionError</span>
</pre></div>
</div>
</div>
<p>An alternative approach is to create a subclass of <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate"><span class="pre">Mock</span></code></a> or
<a class="reference internal" href="unittest.mock.html#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate"><span class="pre">MagicMock</span></code></a> that copies (using <a class="reference internal" href="copy.html#copy.deepcopy" title="copy.deepcopy"><code class="xref py py-func docutils literal notranslate"><span class="pre">copy.deepcopy()</span></code></a>) the arguments.
Here’s an example implementation:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span><span class="w"> </span><span class="nn">copy</span><span class="w"> </span><span class="kn">import</span> <span class="n">deepcopy</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">CopyingMock</span><span class="p">(</span><span class="n">MagicMock</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="fm">__call__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">/</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">args</span> <span class="o">=</span> <span class="n">deepcopy</span><span class="p">(</span><span class="n">args</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">kwargs</span> <span class="o">=</span> <span class="n">deepcopy</span><span class="p">(</span><span class="n">kwargs</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">return</span> <span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="fm">__call__</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">c</span> <span class="o">=</span> <span class="n">CopyingMock</span><span class="p">(</span><span class="n">return_value</span><span class="o">=</span><span class="kc">None</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">arg</span> <span class="o">=</span> <span class="nb">set</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">c</span><span class="p">(</span><span class="n">arg</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">arg</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">c</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">(</span><span class="nb">set</span><span class="p">())</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">c</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">(</span><span class="n">arg</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="w"> </span><span class="o">...</span>
<span class="gr">AssertionError</span>: <span class="n">expected call not found.</span>
<span class="x">Expected: mock({1})</span>
<span class="x">Actual: mock(set())</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">c</span><span class="o">.</span><span class="n">foo</span>
<span class="go">&lt;CopyingMock name=&#39;mock.foo&#39; id=&#39;...&#39;&gt;</span>
</pre></div>
</div>
<p>When you subclass <code class="docutils literal notranslate"><span class="pre">Mock</span></code> or <code class="docutils literal notranslate"><span class="pre">MagicMock</span></code> all dynamically created attributes,
and the <code class="docutils literal notranslate"><span class="pre">return_value</span></code> will use your subclass automatically. That means all
children of a <code class="docutils literal notranslate"><span class="pre">CopyingMock</span></code> will also have the type <code class="docutils literal notranslate"><span class="pre">CopyingMock</span></code>.</p>
</section>
<section id="nesting-patches">
<h3>Nesting Patches<a class="headerlink" href="#nesting-patches" title="Link to this heading"></a></h3>
<p>Using patch as a context manager is nice, but if you do multiple patches you
can end up with nested with statements indenting further and further to the
right:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">MyTest</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">test_foo</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s1">&#39;mymodule.Foo&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">mock_foo</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s1">&#39;mymodule.Bar&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">mock_bar</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s1">&#39;mymodule.Spam&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">mock_spam</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">mymodule</span><span class="o">.</span><span class="n">Foo</span> <span class="ow">is</span> <span class="n">mock_foo</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">mymodule</span><span class="o">.</span><span class="n">Bar</span> <span class="ow">is</span> <span class="n">mock_bar</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">mymodule</span><span class="o">.</span><span class="n">Spam</span> <span class="ow">is</span> <span class="n">mock_spam</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">original</span> <span class="o">=</span> <span class="n">mymodule</span><span class="o">.</span><span class="n">Foo</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">MyTest</span><span class="p">(</span><span class="s1">&#39;test_foo&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">test_foo</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">assert</span> <span class="n">mymodule</span><span class="o">.</span><span class="n">Foo</span> <span class="ow">is</span> <span class="n">original</span>
</pre></div>
</div>
<p>With unittest <code class="docutils literal notranslate"><span class="pre">cleanup</span></code> functions and the <a class="reference internal" href="unittest.mock.html#start-and-stop"><span class="std std-ref">patch methods: start and stop</span></a> we can
achieve the same effect without the nested indentation. A simple helper
method, <code class="docutils literal notranslate"><span class="pre">create_patch</span></code>, puts the patch in place and returns the created mock
for us:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">MyTest</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">create_patch</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">patcher</span> <span class="o">=</span> <span class="n">patch</span><span class="p">(</span><span class="n">name</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">thing</span> <span class="o">=</span> <span class="n">patcher</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">addCleanup</span><span class="p">(</span><span class="n">patcher</span><span class="o">.</span><span class="n">stop</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">thing</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">test_foo</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">mock_foo</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">create_patch</span><span class="p">(</span><span class="s1">&#39;mymodule.Foo&#39;</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">mock_bar</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">create_patch</span><span class="p">(</span><span class="s1">&#39;mymodule.Bar&#39;</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">mock_spam</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">create_patch</span><span class="p">(</span><span class="s1">&#39;mymodule.Spam&#39;</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">mymodule</span><span class="o">.</span><span class="n">Foo</span> <span class="ow">is</span> <span class="n">mock_foo</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">mymodule</span><span class="o">.</span><span class="n">Bar</span> <span class="ow">is</span> <span class="n">mock_bar</span>
<span class="gp">... </span> <span class="k">assert</span> <span class="n">mymodule</span><span class="o">.</span><span class="n">Spam</span> <span class="ow">is</span> <span class="n">mock_spam</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">original</span> <span class="o">=</span> <span class="n">mymodule</span><span class="o">.</span><span class="n">Foo</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">MyTest</span><span class="p">(</span><span class="s1">&#39;test_foo&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">run</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">assert</span> <span class="n">mymodule</span><span class="o">.</span><span class="n">Foo</span> <span class="ow">is</span> <span class="n">original</span>
</pre></div>
</div>
</section>
<section id="mocking-a-dictionary-with-magicmock">
<h3>Mocking a dictionary with MagicMock<a class="headerlink" href="#mocking-a-dictionary-with-magicmock" title="Link to this heading"></a></h3>
<p>You may want to mock a dictionary, or other container object, recording all
access to it whilst having it still behave like a dictionary.</p>
<p>We can do this with <a class="reference internal" href="unittest.mock.html#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate"><span class="pre">MagicMock</span></code></a>, which will behave like a dictionary,
and using <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-data docutils literal notranslate"><span class="pre">side_effect</span></code></a> to delegate dictionary access to a real
underlying dictionary that is under our control.</p>
<p>When the <a class="reference internal" href="../reference/datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getitem__()</span></code></a> and <a class="reference internal" href="../reference/datamodel.html#object.__setitem__" title="object.__setitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__setitem__()</span></code></a> methods
of our <code class="docutils literal notranslate"><span class="pre">MagicMock</span></code> are called
(normal dictionary access) then <code class="docutils literal notranslate"><span class="pre">side_effect</span></code> is called with the key (and in
the case of <code class="docutils literal notranslate"><span class="pre">__setitem__</span></code> the value too). We can also control what is returned.</p>
<p>After the <code class="docutils literal notranslate"><span class="pre">MagicMock</span></code> has been used we can use attributes like
<a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.call_args_list" title="unittest.mock.Mock.call_args_list"><code class="xref py py-data docutils literal notranslate"><span class="pre">call_args_list</span></code></a> to assert about how the dictionary was used:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">my_dict</span> <span class="o">=</span> <span class="p">{</span><span class="s1">&#39;a&#39;</span><span class="p">:</span> <span class="mi">1</span><span class="p">,</span> <span class="s1">&#39;b&#39;</span><span class="p">:</span> <span class="mi">2</span><span class="p">,</span> <span class="s1">&#39;c&#39;</span><span class="p">:</span> <span class="mi">3</span><span class="p">}</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">def</span><span class="w"> </span><span class="nf">getitem</span><span class="p">(</span><span class="n">name</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">my_dict</span><span class="p">[</span><span class="n">name</span><span class="p">]</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">def</span><span class="w"> </span><span class="nf">setitem</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">val</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">my_dict</span><span class="p">[</span><span class="n">name</span><span class="p">]</span> <span class="o">=</span> <span class="n">val</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="fm">__getitem__</span><span class="o">.</span><span class="n">side_effect</span> <span class="o">=</span> <span class="n">getitem</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="fm">__setitem__</span><span class="o">.</span><span class="n">side_effect</span> <span class="o">=</span> <span class="n">setitem</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>An alternative to using <code class="docutils literal notranslate"><span class="pre">MagicMock</span></code> is to use <code class="docutils literal notranslate"><span class="pre">Mock</span></code> and <em>only</em> provide
the magic methods you specifically want:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="fm">__getitem__</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">(</span><span class="n">side_effect</span><span class="o">=</span><span class="n">getitem</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="fm">__setitem__</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">(</span><span class="n">side_effect</span><span class="o">=</span><span class="n">setitem</span><span class="p">)</span>
</pre></div>
</div>
<p>A <em>third</em> option is to use <code class="docutils literal notranslate"><span class="pre">MagicMock</span></code> but passing in <code class="docutils literal notranslate"><span class="pre">dict</span></code> as the <em>spec</em>
(or <em>spec_set</em>) argument so that the <code class="docutils literal notranslate"><span class="pre">MagicMock</span></code> created only has
dictionary magic methods available:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">(</span><span class="n">spec_set</span><span class="o">=</span><span class="nb">dict</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="fm">__getitem__</span><span class="o">.</span><span class="n">side_effect</span> <span class="o">=</span> <span class="n">getitem</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="fm">__setitem__</span><span class="o">.</span><span class="n">side_effect</span> <span class="o">=</span> <span class="n">setitem</span>
</pre></div>
</div>
</div>
<p>With these side effect functions in place, the <code class="docutils literal notranslate"><span class="pre">mock</span></code> will behave like a normal
dictionary but recording the access. It even raises a <a class="reference internal" href="exceptions.html#KeyError" title="KeyError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyError</span></code></a> if you try
to access a key that doesn’t exist.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">[</span><span class="s1">&#39;a&#39;</span><span class="p">]</span>
<span class="go">1</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">[</span><span class="s1">&#39;c&#39;</span><span class="p">]</span>
<span class="go">3</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">[</span><span class="s1">&#39;d&#39;</span><span class="p">]</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="w"> </span><span class="o">...</span>
<span class="gr">KeyError</span>: <span class="n">&#39;d&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">[</span><span class="s1">&#39;b&#39;</span><span class="p">]</span> <span class="o">=</span> <span class="s1">&#39;fish&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">[</span><span class="s1">&#39;d&#39;</span><span class="p">]</span> <span class="o">=</span> <span class="s1">&#39;eggs&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">[</span><span class="s1">&#39;b&#39;</span><span class="p">]</span>
<span class="go">&#39;fish&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">[</span><span class="s1">&#39;d&#39;</span><span class="p">]</span>
<span class="go">&#39;eggs&#39;</span>
</pre></div>
</div>
<p>After it has been used you can make assertions about the access using the normal
mock methods and attributes:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="fm">__getitem__</span><span class="o">.</span><span class="n">call_args_list</span>
<span class="go">[call(&#39;a&#39;), call(&#39;c&#39;), call(&#39;d&#39;), call(&#39;b&#39;), call(&#39;d&#39;)]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="fm">__setitem__</span><span class="o">.</span><span class="n">call_args_list</span>
<span class="go">[call(&#39;b&#39;, &#39;fish&#39;), call(&#39;d&#39;, &#39;eggs&#39;)]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">my_dict</span>
<span class="go">{&#39;a&#39;: 1, &#39;b&#39;: &#39;fish&#39;, &#39;c&#39;: 3, &#39;d&#39;: &#39;eggs&#39;}</span>
</pre></div>
</div>
</section>
<section id="mock-subclasses-and-their-attributes">
<h3>Mock subclasses and their attributes<a class="headerlink" href="#mock-subclasses-and-their-attributes" title="Link to this heading"></a></h3>
<p>There are various reasons why you might want to subclass <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate"><span class="pre">Mock</span></code></a>. One
reason might be to add helper methods. Here’s a silly example:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">MyMock</span><span class="p">(</span><span class="n">MagicMock</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">has_been_called</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">called</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mymock</span> <span class="o">=</span> <span class="n">MyMock</span><span class="p">(</span><span class="n">return_value</span><span class="o">=</span><span class="kc">None</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mymock</span>
<span class="go">&lt;MyMock id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mymock</span><span class="o">.</span><span class="n">has_been_called</span><span class="p">()</span>
<span class="go">False</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mymock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mymock</span><span class="o">.</span><span class="n">has_been_called</span><span class="p">()</span>
<span class="go">True</span>
</pre></div>
</div>
<p>The standard behaviour for <code class="docutils literal notranslate"><span class="pre">Mock</span></code> instances is that attributes and the return
value mocks are of the same type as the mock they are accessed on. This ensures
that <code class="docutils literal notranslate"><span class="pre">Mock</span></code> attributes are <code class="docutils literal notranslate"><span class="pre">Mocks</span></code> and <code class="docutils literal notranslate"><span class="pre">MagicMock</span></code> attributes are <code class="docutils literal notranslate"><span class="pre">MagicMocks</span></code>
<a class="footnote-reference brackets" href="#id5" id="id4" role="doc-noteref"><span class="fn-bracket">[</span>2<span class="fn-bracket">]</span></a>. So if you’re subclassing to add helper methods then they’ll also be
available on the attributes and return value mock of instances of your
subclass.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mymock</span><span class="o">.</span><span class="n">foo</span>
<span class="go">&lt;MyMock name=&#39;mock.foo&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mymock</span><span class="o">.</span><span class="n">foo</span><span class="o">.</span><span class="n">has_been_called</span><span class="p">()</span>
<span class="go">False</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mymock</span><span class="o">.</span><span class="n">foo</span><span class="p">()</span>
<span class="go">&lt;MyMock name=&#39;mock.foo()&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mymock</span><span class="o">.</span><span class="n">foo</span><span class="o">.</span><span class="n">has_been_called</span><span class="p">()</span>
<span class="go">True</span>
</pre></div>
</div>
<p>Sometimes this is inconvenient. For example, <a class="reference external" href="https://code.google.com/archive/p/mock/issues/105">one user</a> is subclassing mock to
created a <a class="reference external" href="https://twisted.org/documents/11.0.0/api/twisted.python.components.html">Twisted adaptor</a>.
Having this applied to attributes too actually causes errors.</p>
<p><code class="docutils literal notranslate"><span class="pre">Mock</span></code> (in all its flavours) uses a method called <code class="docutils literal notranslate"><span class="pre">_get_child_mock</span></code> to create
these “sub-mocks” for attributes and return values. You can prevent your
subclass being used for attributes by overriding this method. The signature is
that it takes arbitrary keyword arguments (<code class="docutils literal notranslate"><span class="pre">**kwargs</span></code>) which are then passed
onto the mock constructor:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">Subclass</span><span class="p">(</span><span class="n">MagicMock</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">_get_child_mock</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">/</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">MagicMock</span><span class="p">(</span><span class="o">**</span><span class="n">kwargs</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mymock</span> <span class="o">=</span> <span class="n">Subclass</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mymock</span><span class="o">.</span><span class="n">foo</span>
<span class="go">&lt;MagicMock name=&#39;mock.foo&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">mymock</span><span class="p">,</span> <span class="n">Subclass</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">assert</span> <span class="ow">not</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">mymock</span><span class="o">.</span><span class="n">foo</span><span class="p">,</span> <span class="n">Subclass</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">assert</span> <span class="ow">not</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">mymock</span><span class="p">(),</span> <span class="n">Subclass</span><span class="p">)</span>
</pre></div>
</div>
<aside class="footnote-list brackets">
<aside class="footnote brackets" id="id5" role="doc-footnote">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id4">2</a><span class="fn-bracket">]</span></span>
<p>An exception to this rule are the non-callable mocks. Attributes use the
callable variant because otherwise non-callable mocks couldn’t have callable
methods.</p>
</aside>
</aside>
</section>
<section id="mocking-imports-with-patch-dict">
<h3>Mocking imports with patch.dict<a class="headerlink" href="#mocking-imports-with-patch-dict" title="Link to this heading"></a></h3>
<p>One situation where mocking can be hard is where you have a local import inside
a function. These are harder to mock because they aren’t using an object from
the module namespace that we can patch out.</p>
<p>Generally local imports are to be avoided. They are sometimes done to prevent
circular dependencies, for which there is <em>usually</em> a much better way to solve
the problem (refactor the code) or to prevent “up front costs” by delaying the
import. This can also be solved in better ways than an unconditional local
import (store the module as a class or module attribute and only do the import
on first use).</p>
<p>That aside there is a way to use <code class="docutils literal notranslate"><span class="pre">mock</span></code> to affect the results of an import.
Importing fetches an <em>object</em> from the <a class="reference internal" href="sys.html#sys.modules" title="sys.modules"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.modules</span></code></a> dictionary. Note that it
fetches an <em>object</em>, which need not be a module. Importing a module for the
first time results in a module object being put in <code class="docutils literal notranslate"><span class="pre">sys.modules</span></code>, so usually
when you import something you get a module back. This need not be the case
however.</p>
<p>This means you can use <a class="reference internal" href="unittest.mock.html#unittest.mock.patch.dict" title="unittest.mock.patch.dict"><code class="xref py py-func docutils literal notranslate"><span class="pre">patch.dict()</span></code></a> to <em>temporarily</em> put a mock in place
in <a class="reference internal" href="sys.html#sys.modules" title="sys.modules"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.modules</span></code></a>. Any imports whilst this patch is active will fetch the mock.
When the patch is complete (the decorated function exits, the with statement
body is complete or <code class="docutils literal notranslate"><span class="pre">patcher.stop()</span></code> is called) then whatever was there
previously will be restored safely.</p>
<p>Here’s an example that mocks out the ‘fooble’ module.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span><span class="w"> </span><span class="nn">sys</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">patch</span><span class="o">.</span><span class="n">dict</span><span class="p">(</span><span class="s1">&#39;sys.modules&#39;</span><span class="p">,</span> <span class="p">{</span><span class="s1">&#39;fooble&#39;</span><span class="p">:</span> <span class="n">mock</span><span class="p">}):</span>
<span class="gp">... </span> <span class="kn">import</span><span class="w"> </span><span class="nn">fooble</span>
<span class="gp">... </span> <span class="n">fooble</span><span class="o">.</span><span class="n">blob</span><span class="p">()</span>
<span class="gp">...</span>
<span class="go">&lt;Mock name=&#39;mock.blob()&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">assert</span> <span class="s1">&#39;fooble&#39;</span> <span class="ow">not</span> <span class="ow">in</span> <span class="n">sys</span><span class="o">.</span><span class="n">modules</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">blob</span><span class="o">.</span><span class="n">assert_called_once_with</span><span class="p">()</span>
</pre></div>
</div>
<p>As you can see the <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">fooble</span></code> succeeds, but on exit there is no ‘fooble’
left in <a class="reference internal" href="sys.html#sys.modules" title="sys.modules"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.modules</span></code></a>.</p>
<p>This also works for the <code class="docutils literal notranslate"><span class="pre">from</span> <span class="pre">module</span> <span class="pre">import</span> <span class="pre">name</span></code> form:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">patch</span><span class="o">.</span><span class="n">dict</span><span class="p">(</span><span class="s1">&#39;sys.modules&#39;</span><span class="p">,</span> <span class="p">{</span><span class="s1">&#39;fooble&#39;</span><span class="p">:</span> <span class="n">mock</span><span class="p">}):</span>
<span class="gp">... </span> <span class="kn">from</span><span class="w"> </span><span class="nn">fooble</span><span class="w"> </span><span class="kn">import</span> <span class="n">blob</span>
<span class="gp">... </span> <span class="n">blob</span><span class="o">.</span><span class="n">blip</span><span class="p">()</span>
<span class="gp">...</span>
<span class="go">&lt;Mock name=&#39;mock.blob.blip()&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">blob</span><span class="o">.</span><span class="n">blip</span><span class="o">.</span><span class="n">assert_called_once_with</span><span class="p">()</span>
</pre></div>
</div>
<p>With slightly more work you can also mock package imports:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">modules</span> <span class="o">=</span> <span class="p">{</span><span class="s1">&#39;package&#39;</span><span class="p">:</span> <span class="n">mock</span><span class="p">,</span> <span class="s1">&#39;package.module&#39;</span><span class="p">:</span> <span class="n">mock</span><span class="o">.</span><span class="n">module</span><span class="p">}</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">patch</span><span class="o">.</span><span class="n">dict</span><span class="p">(</span><span class="s1">&#39;sys.modules&#39;</span><span class="p">,</span> <span class="n">modules</span><span class="p">):</span>
<span class="gp">... </span> <span class="kn">from</span><span class="w"> </span><span class="nn">package.module</span><span class="w"> </span><span class="kn">import</span> <span class="n">fooble</span>
<span class="gp">... </span> <span class="n">fooble</span><span class="p">()</span>
<span class="gp">...</span>
<span class="go">&lt;Mock name=&#39;mock.module.fooble()&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">module</span><span class="o">.</span><span class="n">fooble</span><span class="o">.</span><span class="n">assert_called_once_with</span><span class="p">()</span>
</pre></div>
</div>
</section>
<section id="tracking-order-of-calls-and-less-verbose-call-assertions">
<h3>Tracking order of calls and less verbose call assertions<a class="headerlink" href="#tracking-order-of-calls-and-less-verbose-call-assertions" title="Link to this heading"></a></h3>
<p>The <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate"><span class="pre">Mock</span></code></a> class allows you to track the <em>order</em> of method calls on
your mock objects through the <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.method_calls" title="unittest.mock.Mock.method_calls"><code class="xref py py-attr docutils literal notranslate"><span class="pre">method_calls</span></code></a> attribute. This
doesn’t allow you to track the order of calls between separate mock objects,
however we can use <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate"><span class="pre">mock_calls</span></code></a> to achieve the same effect.</p>
<p>Because mocks track calls to child mocks in <code class="docutils literal notranslate"><span class="pre">mock_calls</span></code>, and accessing an
arbitrary attribute of a mock creates a child mock, we can create our separate
mocks from a parent one. Calls to those child mock will then all be recorded,
in order, in the <code class="docutils literal notranslate"><span class="pre">mock_calls</span></code> of the parent:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">manager</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_foo</span> <span class="o">=</span> <span class="n">manager</span><span class="o">.</span><span class="n">foo</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_bar</span> <span class="o">=</span> <span class="n">manager</span><span class="o">.</span><span class="n">bar</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">mock_foo</span><span class="o">.</span><span class="n">something</span><span class="p">()</span>
<span class="go">&lt;Mock name=&#39;mock.foo.something()&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock_bar</span><span class="o">.</span><span class="n">other</span><span class="o">.</span><span class="n">thing</span><span class="p">()</span>
<span class="go">&lt;Mock name=&#39;mock.bar.other.thing()&#39; id=&#39;...&#39;&gt;</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">manager</span><span class="o">.</span><span class="n">mock_calls</span>
<span class="go">[call.foo.something(), call.bar.other.thing()]</span>
</pre></div>
</div>
<p>We can then assert about the calls, including the order, by comparing with
the <code class="docutils literal notranslate"><span class="pre">mock_calls</span></code> attribute on the manager mock:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">expected_calls</span> <span class="o">=</span> <span class="p">[</span><span class="n">call</span><span class="o">.</span><span class="n">foo</span><span class="o">.</span><span class="n">something</span><span class="p">(),</span> <span class="n">call</span><span class="o">.</span><span class="n">bar</span><span class="o">.</span><span class="n">other</span><span class="o">.</span><span class="n">thing</span><span class="p">()]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">manager</span><span class="o">.</span><span class="n">mock_calls</span> <span class="o">==</span> <span class="n">expected_calls</span>
<span class="go">True</span>
</pre></div>
</div>
<p>If <code class="docutils literal notranslate"><span class="pre">patch</span></code> is creating, and putting in place, your mocks then you can attach
them to a manager mock using the <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.attach_mock" title="unittest.mock.Mock.attach_mock"><code class="xref py py-meth docutils literal notranslate"><span class="pre">attach_mock()</span></code></a> method. After
attaching calls will be recorded in <code class="docutils literal notranslate"><span class="pre">mock_calls</span></code> of the manager.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">manager</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s1">&#39;mymodule.Class1&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">MockClass1</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s1">&#39;mymodule.Class2&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">MockClass2</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">manager</span><span class="o">.</span><span class="n">attach_mock</span><span class="p">(</span><span class="n">MockClass1</span><span class="p">,</span> <span class="s1">&#39;MockClass1&#39;</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">manager</span><span class="o">.</span><span class="n">attach_mock</span><span class="p">(</span><span class="n">MockClass2</span><span class="p">,</span> <span class="s1">&#39;MockClass2&#39;</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">MockClass1</span><span class="p">()</span><span class="o">.</span><span class="n">foo</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">MockClass2</span><span class="p">()</span><span class="o">.</span><span class="n">bar</span><span class="p">()</span>
<span class="go">&lt;MagicMock name=&#39;mock.MockClass1().foo()&#39; id=&#39;...&#39;&gt;</span>
<span class="go">&lt;MagicMock name=&#39;mock.MockClass2().bar()&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">manager</span><span class="o">.</span><span class="n">mock_calls</span>
<span class="go">[call.MockClass1(),</span>
<span class="go">call.MockClass1().foo(),</span>
<span class="go">call.MockClass2(),</span>
<span class="go">call.MockClass2().bar()]</span>
</pre></div>
</div>
<p>If many calls have been made, but you’re only interested in a particular
sequence of them then an alternative is to use the
<a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.assert_has_calls" title="unittest.mock.Mock.assert_has_calls"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assert_has_calls()</span></code></a> method. This takes a list of calls (constructed
with the <a class="reference internal" href="unittest.mock.html#unittest.mock.call" title="unittest.mock.call"><code class="xref py py-data docutils literal notranslate"><span class="pre">call</span></code></a> object). If that sequence of calls are in
<a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate"><span class="pre">mock_calls</span></code></a> then the assert succeeds.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="p">()</span><span class="o">.</span><span class="n">foo</span><span class="p">()</span><span class="o">.</span><span class="n">bar</span><span class="p">()</span><span class="o">.</span><span class="n">baz</span><span class="p">()</span>
<span class="go">&lt;MagicMock name=&#39;mock().foo().bar().baz()&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">one</span><span class="p">()</span><span class="o">.</span><span class="n">two</span><span class="p">()</span><span class="o">.</span><span class="n">three</span><span class="p">()</span>
<span class="go">&lt;MagicMock name=&#39;mock.one().two().three()&#39; id=&#39;...&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">calls</span> <span class="o">=</span> <span class="n">call</span><span class="o">.</span><span class="n">one</span><span class="p">()</span><span class="o">.</span><span class="n">two</span><span class="p">()</span><span class="o">.</span><span class="n">three</span><span class="p">()</span><span class="o">.</span><span class="n">call_list</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">assert_has_calls</span><span class="p">(</span><span class="n">calls</span><span class="p">)</span>
</pre></div>
</div>
<p>Even though the chained call <code class="docutils literal notranslate"><span class="pre">m.one().two().three()</span></code> aren’t the only calls that
have been made to the mock, the assert still succeeds.</p>
<p>Sometimes a mock may have several calls made to it, and you are only interested
in asserting about <em>some</em> of those calls. You may not even care about the
order. In this case you can pass <code class="docutils literal notranslate"><span class="pre">any_order=True</span></code> to <code class="docutils literal notranslate"><span class="pre">assert_has_calls</span></code>:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="p">(</span><span class="mi">1</span><span class="p">),</span> <span class="n">m</span><span class="o">.</span><span class="n">two</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">),</span> <span class="n">m</span><span class="o">.</span><span class="n">seven</span><span class="p">(</span><span class="mi">7</span><span class="p">),</span> <span class="n">m</span><span class="o">.</span><span class="n">fifty</span><span class="p">(</span><span class="s1">&#39;50&#39;</span><span class="p">)</span>
<span class="go">(...)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">calls</span> <span class="o">=</span> <span class="p">[</span><span class="n">call</span><span class="o">.</span><span class="n">fifty</span><span class="p">(</span><span class="s1">&#39;50&#39;</span><span class="p">),</span> <span class="n">call</span><span class="p">(</span><span class="mi">1</span><span class="p">),</span> <span class="n">call</span><span class="o">.</span><span class="n">seven</span><span class="p">(</span><span class="mi">7</span><span class="p">)]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">assert_has_calls</span><span class="p">(</span><span class="n">calls</span><span class="p">,</span> <span class="n">any_order</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
</pre></div>
</div>
</section>
<section id="more-complex-argument-matching">
<h3>More complex argument matching<a class="headerlink" href="#more-complex-argument-matching" title="Link to this heading"></a></h3>
<p>Using the same basic concept as <a class="reference internal" href="unittest.mock.html#unittest.mock.ANY" title="unittest.mock.ANY"><code class="xref py py-data docutils literal notranslate"><span class="pre">ANY</span></code></a> we can implement matchers to do more
complex assertions on objects used as arguments to mocks.</p>
<p>Suppose we expect some object to be passed to a mock that by default
compares equal based on object identity (which is the Python default for user
defined classes). To use <a class="reference internal" href="unittest.mock.html#unittest.mock.Mock.assert_called_with" title="unittest.mock.Mock.assert_called_with"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assert_called_with()</span></code></a> we would need to pass
in the exact same object. If we are only interested in some of the attributes
of this object then we can create a matcher that will check these attributes
for us.</p>
<p>You can see in this example how a ‘standard’ call to <code class="docutils literal notranslate"><span class="pre">assert_called_with</span></code> isn’t
sufficient:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">Foo</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">a</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">b</span> <span class="o">=</span> <span class="n">a</span><span class="p">,</span> <span class="n">b</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">(</span><span class="n">return_value</span><span class="o">=</span><span class="kc">None</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="p">(</span><span class="n">Foo</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">))</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">(</span><span class="n">Foo</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">))</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="w"> </span><span class="o">...</span>
<span class="gr">AssertionError</span>: <span class="n">expected call not found.</span>
<span class="x">Expected: mock(&lt;__main__.Foo object at 0x...&gt;)</span>
<span class="x">Actual: mock(&lt;__main__.Foo object at 0x...&gt;)</span>
</pre></div>
</div>
<p>A comparison function for our <code class="docutils literal notranslate"><span class="pre">Foo</span></code> class might look something like this:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span><span class="w"> </span><span class="nf">compare</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">other</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">if</span> <span class="ow">not</span> <span class="nb">type</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span> <span class="o">==</span> <span class="nb">type</span><span class="p">(</span><span class="n">other</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="kc">False</span>
<span class="gp">... </span> <span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">a</span> <span class="o">!=</span> <span class="n">other</span><span class="o">.</span><span class="n">a</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">return</span> <span class="kc">False</span>
<span class="gp">... </span> <span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">b</span> <span class="o">!=</span> <span class="n">other</span><span class="o">.</span><span class="n">b</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">return</span> <span class="kc">False</span>
<span class="gp">... </span> <span class="k">return</span> <span class="kc">True</span>
<span class="gp">...</span>
</pre></div>
</div>
<p>And a matcher object that can use comparison functions like this for its
equality operation would look something like this:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span><span class="w"> </span><span class="nc">Matcher</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">compare</span><span class="p">,</span> <span class="n">some_obj</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">compare</span> <span class="o">=</span> <span class="n">compare</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">some_obj</span> <span class="o">=</span> <span class="n">some_obj</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="fm">__eq__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">other</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">compare</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">some_obj</span><span class="p">,</span> <span class="n">other</span><span class="p">)</span>
<span class="gp">...</span>
</pre></div>
</div>
<p>Putting all this together:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">match_foo</span> <span class="o">=</span> <span class="n">Matcher</span><span class="p">(</span><span class="n">compare</span><span class="p">,</span> <span class="n">Foo</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">))</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">(</span><span class="n">match_foo</span><span class="p">)</span>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">Matcher</span></code> is instantiated with our compare function and the <code class="docutils literal notranslate"><span class="pre">Foo</span></code> object
we want to compare against. In <code class="docutils literal notranslate"><span class="pre">assert_called_with</span></code> the <code class="docutils literal notranslate"><span class="pre">Matcher</span></code> equality
method will be called, which compares the object the mock was called with
against the one we created our matcher with. If they match then
<code class="docutils literal notranslate"><span class="pre">assert_called_with</span></code> passes, and if they don’t an <a class="reference internal" href="exceptions.html#AssertionError" title="AssertionError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">AssertionError</span></code></a> is raised:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">match_wrong</span> <span class="o">=</span> <span class="n">Matcher</span><span class="p">(</span><span class="n">compare</span><span class="p">,</span> <span class="n">Foo</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">))</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">mock</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">(</span><span class="n">match_wrong</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="w"> </span><span class="o">...</span>
<span class="gr">AssertionError</span>: <span class="n">Expected: ((&lt;Matcher object at 0x...&gt;,), {})</span>
<span class="x">Called with: ((&lt;Foo object at 0x...&gt;,), {})</span>
</pre></div>
</div>
<p>With a bit of tweaking you could have the comparison function raise the
<a class="reference internal" href="exceptions.html#AssertionError" title="AssertionError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">AssertionError</span></code></a> directly and provide a more useful failure message.</p>
<p>As of version 1.5, the Python testing library <a class="reference external" href="https://pyhamcrest.readthedocs.io/">PyHamcrest</a> provides similar functionality,
that may be useful here, in the form of its equality matcher
(<a class="reference external" href="https://pyhamcrest.readthedocs.io/en/release-1.8/integration/#module-hamcrest.library.integration.match_equality">hamcrest.library.integration.match_equality</a>).</p>
</section>
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<ul>
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">unittest.mock</span></code> — getting started</a><ul>
<li><a class="reference internal" href="#using-mock">Using Mock</a><ul>
<li><a class="reference internal" href="#mock-patching-methods">Mock Patching Methods</a></li>
<li><a class="reference internal" href="#mock-for-method-calls-on-an-object">Mock for Method Calls on an Object</a></li>
<li><a class="reference internal" href="#mocking-classes">Mocking Classes</a></li>
<li><a class="reference internal" href="#naming-your-mocks">Naming your mocks</a></li>
<li><a class="reference internal" href="#tracking-all-calls">Tracking all Calls</a></li>
<li><a class="reference internal" href="#setting-return-values-and-attributes">Setting Return Values and Attributes</a></li>
<li><a class="reference internal" href="#raising-exceptions-with-mocks">Raising exceptions with mocks</a></li>
<li><a class="reference internal" href="#side-effect-functions-and-iterables">Side effect functions and iterables</a></li>
<li><a class="reference internal" href="#mocking-asynchronous-iterators">Mocking asynchronous iterators</a></li>
<li><a class="reference internal" href="#mocking-asynchronous-context-manager">Mocking asynchronous context manager</a></li>
<li><a class="reference internal" href="#creating-a-mock-from-an-existing-object">Creating a Mock from an Existing Object</a></li>
<li><a class="reference internal" href="#using-side-effect-to-return-per-file-content">Using side_effect to return per file content</a></li>
</ul>
</li>
<li><a class="reference internal" href="#patch-decorators">Patch Decorators</a></li>
<li><a class="reference internal" href="#further-examples">Further Examples</a><ul>
<li><a class="reference internal" href="#mocking-chained-calls">Mocking chained calls</a></li>
<li><a class="reference internal" href="#partial-mocking">Partial mocking</a></li>
<li><a class="reference internal" href="#mocking-a-generator-method">Mocking a Generator Method</a></li>
<li><a class="reference internal" href="#applying-the-same-patch-to-every-test-method">Applying the same patch to every test method</a></li>
<li><a class="reference internal" href="#mocking-unbound-methods">Mocking Unbound Methods</a></li>
<li><a class="reference internal" href="#checking-multiple-calls-with-mock">Checking multiple calls with mock</a></li>
<li><a class="reference internal" href="#coping-with-mutable-arguments">Coping with mutable arguments</a></li>
<li><a class="reference internal" href="#nesting-patches">Nesting Patches</a></li>
<li><a class="reference internal" href="#mocking-a-dictionary-with-magicmock">Mocking a dictionary with MagicMock</a></li>
<li><a class="reference internal" href="#mock-subclasses-and-their-attributes">Mock subclasses and their attributes</a></li>
<li><a class="reference internal" href="#mocking-imports-with-patch-dict">Mocking imports with patch.dict</a></li>
<li><a class="reference internal" href="#tracking-order-of-calls-and-less-verbose-call-assertions">Tracking order of calls and less verbose call assertions</a></li>
<li><a class="reference internal" href="#more-complex-argument-matching">More complex argument matching</a></li>
</ul>
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</ul>
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