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| <div class="section" id="getting-started-with-mock"> |
| <h1>Getting Started with Mock<a class="headerlink" href="#getting-started-with-mock" title="Permalink to this headline">¶</a></h1> |
| <span class="target" id="getting-started"></span><span class="target" id="index-0"></span><div class="section" id="using-mock"> |
| <h2>Using Mock<a class="headerlink" href="#using-mock" title="Permalink to this headline">¶</a></h2> |
| <div class="section" id="mock-patching-methods"> |
| <h3>Mock Patching Methods<a class="headerlink" href="#mock-patching-methods" title="Permalink to this headline">¶</a></h3> |
| <p>Common uses for <tt class="xref py py-class docutils literal"><span class="pre">Mock</span></tt> objects include:</p> |
| <ul class="simple"> |
| <li>Patching methods</li> |
| <li>Recording method calls on objects</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="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">real</span> <span class="o">=</span> <span class="n">SomeClass</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="o">=</span> <span class="n">MagicMock</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s">'method'</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">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="s">'value'</span><span class="p">)</span> |
| <span class="go"><MagicMock name='method()' id='...'></span> |
| </pre></div> |
| </div> |
| <p>Once our mock has been used (<cite>real.method</cite> 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="first admonition-title">Note</p> |
| <p class="last">In most of these examples the <tt class="xref py py-class docutils literal"><span class="pre">Mock</span></tt> and <tt class="xref py py-class docutils literal"><span class="pre">MagicMock</span></tt> classes |
| are interchangeable. As the <cite>MagicMock</cite> is the more capable class it makes |
| a sensible one to use by default.</p> |
| </div> |
| <p>Once the mock has been called its <tt class="xref py py-attr docutils literal"><span class="pre">called</span></tt> attribute is set to |
| <cite>True</cite>. More importantly we can use the <tt class="xref py py-meth docutils literal"><span class="pre">assert_called_with()</span></tt> or |
| <tt class="xref py py-meth docutils literal"><span class="pre">assert_called_once_with()</span></tt> method to check that it was called with |
| the correct arguments.</p> |
| <p>This example tests that calling <cite>ProductionClass().method</cite> results in a call to |
| the <cite>something</cite> method:</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">mock</span> <span class="kn">import</span> <span class="n">MagicMock</span> |
| <span class="gp">>>> </span><span class="k">class</span> <span class="nc">ProductionClass</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> |
| <span class="gp">... </span> <span class="k">def</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="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">>>> </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">something</span> <span class="o">=</span> <span class="n">MagicMock</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="gp">>>> </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> |
| </div> |
| <div class="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="Permalink to this headline">¶</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 <cite>ProductionClass</cite> below has a <cite>closer</cite> method. If it is called with |
| an object then it calls <cite>close</cite> on it.</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">ProductionClass</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> |
| <span class="gp">... </span> <span class="k">def</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 <cite>close</cite> method and check |
| that it was called correctly.</p> |
| <div class="highlight-python"><div class="highlight"><pre><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">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span> |
| <span class="gp">>>> </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">>>> </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 <tt class="xref py py-meth docutils literal"><span class="pre">assert_called_with()</span></tt> |
| will raise a failure exception.</p> |
| </div> |
| <div class="section" id="mocking-classes"> |
| <h3>Mocking Classes<a class="headerlink" href="#mocking-classes" title="Permalink to this headline">¶</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 <cite>some_function</cite> that instantiates <cite>Foo</cite> |
| and calls a method on it. The call to <cite>patch</cite> replaces the class <cite>Foo</cite> with a |
| mock. The <cite>Foo</cite> instance is the result of calling the mock, so it is configured |
| by modifying the mock <tt class="xref py py-attr docutils literal"><span class="pre">return_value</span></tt>.</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">def</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">>>> </span><span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s">'module.Foo'</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="s">'the result'</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="s">'the result'</span> |
| </pre></div> |
| </div> |
| </div> |
| <div class="section" id="naming-your-mocks"> |
| <h3>Naming your mocks<a class="headerlink" href="#naming-your-mocks" title="Permalink to this headline">¶</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="highlight-python"><div class="highlight"><pre><span class="gp">>>> </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="s">'foo'</span><span class="p">)</span> |
| <span class="gp">>>> </span><span class="n">mock</span> |
| <span class="go"><MagicMock name='foo' id='...'></span> |
| <span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">method</span> |
| <span class="go"><MagicMock name='foo.method' id='...'></span> |
| </pre></div> |
| </div> |
| </div> |
| <div class="section" id="tracking-all-calls"> |
| <h3>Tracking all Calls<a class="headerlink" href="#tracking-all-calls" title="Permalink to this headline">¶</a></h3> |
| <p>Often you want to track more than a single call to a method. The |
| <tt class="xref py py-attr docutils literal"><span class="pre">mock_calls</span></tt> attribute records all calls |
| to child attributes of the mock - and also to their children.</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">mock</span> <span class="o">=</span> <span class="n">MagicMock</span><span class="p">()</span> |
| <span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">method</span><span class="p">()</span> |
| <span class="go"><MagicMock name='mock.method()' id='...'></span> |
| <span class="gp">>>> </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"><MagicMock name='mock.attribute.method()' id='...'></span> |
| <span class="gp">>>> </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 <cite>mock_calls</cite> 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 <tt class="xref py py-data docutils literal"><span class="pre">call</span></tt> object to construct lists for comparing with |
| <cite>mock_calls</cite>:</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </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">>>> </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> |
| </div> |
| <div class="section" id="setting-return-values-and-attributes"> |
| <h3>Setting Return Values and Attributes<a class="headerlink" href="#setting-return-values-and-attributes" title="Permalink to this headline">¶</a></h3> |
| <p>Setting the return values on a mock object is trivially easy:</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span> |
| <span class="gp">>>> </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">>>> </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="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span> |
| <span class="gp">>>> </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">>>> </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="highlight-python"><div class="highlight"><pre><span class="gp">>>> </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">>>> </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="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span> |
| <span class="gp">>>> </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">>>> </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 |
| <cite>mock.connection.cursor().execute(“SELECT 1”)</cite>. 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 <tt class="xref py py-data docutils literal"><span class="pre">call</span></tt> to construct the set of calls in a “chained call” like |
| this for easy assertion afterwards:</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span> |
| <span class="gp">>>> </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">>>> </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="s">'foo'</span><span class="p">]</span> |
| <span class="gp">>>> </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="s">"SELECT 1"</span><span class="p">)</span> |
| <span class="go">['foo']</span> |
| <span class="gp">>>> </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="s">"SELECT 1"</span><span class="p">)</span><span class="o">.</span><span class="n">call_list</span><span class="p">()</span> |
| <span class="gp">>>> </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('SELECT 1')]</span> |
| <span class="gp">>>> </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 <cite>.call_list()</cite> that turns our call object into a list of |
| calls representing the chained calls.</p> |
| </div> |
| <div class="section" id="raising-exceptions-with-mocks"> |
| <h3>Raising exceptions with mocks<a class="headerlink" href="#raising-exceptions-with-mocks" title="Permalink to this headline">¶</a></h3> |
| <p>A useful attribute is <tt class="xref py py-attr docutils literal"><span class="pre">side_effect</span></tt>. If you set this to an |
| exception class or instance then the exception will be raised when the mock |
| is called.</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </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="s">'Boom!'</span><span class="p">))</span> |
| <span class="gp">>>> </span><span class="n">mock</span><span class="p">()</span> |
| <span class="gt">Traceback (most recent call last):</span> |
| <span class="c">...</span> |
| <span class="gr">Exception</span>: <span class="n">Boom!</span> |
| </pre></div> |
| </div> |
| </div> |
| <div class="section" id="side-effect-functions-and-iterables"> |
| <h3>Side effect functions and iterables<a class="headerlink" href="#side-effect-functions-and-iterables" title="Permalink to this headline">¶</a></h3> |
| <p><cite>side_effect</cite> can also be set to a function or an iterable. The use case for |
| <cite>side_effect</cite> 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 |
| <cite>side_effect</cite> to an iterable every call to the mock returns the next value |
| from the iterable:</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </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">>>> </span><span class="n">mock</span><span class="p">()</span> |
| <span class="go">4</span> |
| <span class="gp">>>> </span><span class="n">mock</span><span class="p">()</span> |
| <span class="go">5</span> |
| <span class="gp">>>> </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, <cite>side_effect</cite> 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="highlight-python"><div class="highlight"><pre><span class="gp">>>> </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">>>> </span><span class="k">def</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">>>> </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">>>> </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">>>> </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> |
| </div> |
| <div class="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="Permalink to this headline">¶</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 <cite>some_method</cite>. In a test for another class, you |
| provide a mock of this object that <em>also</em> provides <cite>some_method</cite>. If later |
| you refactor the first class, so that it no longer has <cite>some_method</cite> - then |
| your tests will continue to pass even though your code is now broken!</p> |
| <p><cite>Mock</cite> allows you to provide an object as a specification for the mock, |
| using the <cite>spec</cite> 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="highlight-python"><div class="highlight"><pre><span class="gp">>>> </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">>>> </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="c">...</span> |
| <span class="gr">AttributeError</span>: <span class="n">object has no attribute 'old_method'</span> |
| </pre></div> |
| </div> |
| <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 |
| <cite>spec_set</cite> instead of <cite>spec</cite>.</p> |
| </div> |
| </div> |
| <div class="section" id="patch-decorators"> |
| <h2>Patch Decorators<a class="headerlink" href="#patch-decorators" title="Permalink to this headline">¶</a></h2> |
| <div class="admonition note"> |
| <p class="first admonition-title">Note</p> |
| <p class="last">With <cite>patch</cite> 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="patch.html#where-to-patch"><em>where to patch</em></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: <cite>patch</cite>, <cite>patch.object</cite> and |
| <cite>patch.dict</cite>. <cite>patch</cite> takes a single string, of the form |
| <cite>package.module.Class.attribute</cite> 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><cite>patch.object</cite>:</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </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">>>> </span><span class="nd">@patch.object</span><span class="p">(</span><span class="n">SomeClass</span><span class="p">,</span> <span class="s">'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="k">def</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">>>> </span><span class="n">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">original</span> |
| |
| <span class="gp">>>> </span><span class="nd">@patch</span><span class="p">(</span><span class="s">'package.module.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="k">def</span> <span class="nf">test</span><span class="p">():</span> |
| <span class="gp">... </span> <span class="kn">from</span> <span class="nn">package.module</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">>>> </span><span class="n">test</span><span class="p">()</span> |
| </pre></div> |
| </div> |
| <p>If you are patching a module (including <cite>__builtin__</cite>) then use <cite>patch</cite> |
| instead of <cite>patch.object</cite>:</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </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">>>> </span><span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s">'__builtin__.open'</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="s">'filename'</span><span class="p">,</span> <span class="s">'r'</span><span class="p">)</span> |
| <span class="gp">...</span> |
| <span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">assert_called_with</span><span class="p">(</span><span class="s">'filename'</span><span class="p">,</span> <span class="s">'r'</span><span class="p">)</span> |
| <span class="gp">>>> </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="s">"incorrect file handle returned"</span> |
| </pre></div> |
| </div> |
| <p>The module name can be ‘dotted’, in the form <cite>package.module</cite> if needed:</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="nd">@patch</span><span class="p">(</span><span class="s">'package.module.ClassName.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="k">def</span> <span class="nf">test</span><span class="p">():</span> |
| <span class="gp">... </span> <span class="kn">from</span> <span class="nn">package.module</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">>>> </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="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">MyTest</span><span class="p">(</span><span class="n">unittest2</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span> |
| <span class="gp">... </span> <span class="nd">@patch.object</span><span class="p">(</span><span class="n">SomeClass</span><span class="p">,</span> <span class="s">'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="k">def</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">>>> </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">>>> </span><span class="n">MyTest</span><span class="p">(</span><span class="s">'test_something'</span><span class="p">)</span><span class="o">.</span><span class="n">test_something</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">original</span> |
| </pre></div> |
| </div> |
| <p>If you want to patch with a Mock, you can use <cite>patch</cite> with only one argument |
| (or <cite>patch.object</cite> with two arguments). The mock will be created for you and |
| passed into the test function / method:</p> |
| <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">MyTest</span><span class="p">(</span><span class="n">unittest2</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span> |
| <span class="gp">... </span> <span class="nd">@patch.object</span><span class="p">(</span><span class="n">SomeClass</span><span class="p">,</span> <span class="s">'static_method'</span><span class="p">)</span> |
| <span class="gp">... </span> <span class="k">def</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">>>> </span><span class="n">MyTest</span><span class="p">(</span><span class="s">'test_something'</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-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">MyTest</span><span class="p">(</span><span class="n">unittest2</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="s">'package.module.ClassName1'</span><span class="p">)</span> |
| <span class="gp">... </span> <span class="nd">@patch</span><span class="p">(</span><span class="s">'package.module.ClassName2'</span><span class="p">)</span> |
| <span class="gp">... </span> <span class="k">def</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">assertTrue</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="ow">is</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">assertTrue</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="ow">is</span> <span class="n">MockClass2</span><span class="p">)</span> |
| <span class="gp">...</span> |
| <span class="gp">>>> </span><span class="n">MyTest</span><span class="p">(</span><span class="s">'test_something'</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 <cite>test_module.ClassName2</cite> is passed in first.</p> |
| <p>There is also <tt class="xref py py-func docutils literal"><span class="pre">patch.dict()</span></tt> 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="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">foo</span> <span class="o">=</span> <span class="p">{</span><span class="s">'key'</span><span class="p">:</span> <span class="s">'value'</span><span class="p">}</span> |
| <span class="gp">>>> </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">>>> </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="s">'newkey'</span><span class="p">:</span> <span class="s">'newvalue'</span><span class="p">},</span> <span class="n">clear</span><span class="o">=</span><span class="bp">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="s">'newkey'</span><span class="p">:</span> <span class="s">'newvalue'</span><span class="p">}</span> |
| <span class="gp">...</span> |
| <span class="gp">>>> </span><span class="k">assert</span> <span class="n">foo</span> <span class="o">==</span> <span class="n">original</span> |
| </pre></div> |
| </div> |
| <p><cite>patch</cite>, <cite>patch.object</cite> and <cite>patch.dict</cite> can all be used as context managers.</p> |
| <p>Where you use <cite>patch</cite> 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="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">ProductionClass</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> |
| <span class="gp">... </span> <span class="k">def</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">>>> </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="s">'method'</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="bp">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">>>> </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 <cite>patch</cite>, <cite>patch.object</cite> and <cite>patch.dict</cite> can be used as |
| class decorators. When used in this way it is the same as applying the |
| decorator indvidually to every method whose name starts with “test”.</p> |
| <p>For some more advanced examples, see the <a class="reference internal" href="examples.html#further-examples"><em>Further Examples</em></a> page.</p> |
| </div> |
| </div> |
| |
| |
| </div> |
| </div> |
| </div> |
| <div class="sphinxsidebar"> |
| <div class="sphinxsidebarwrapper"> |
| <h3><a href="index.html">Table Of Contents</a></h3> |
| <ul> |
| <li><a class="reference internal" href="#">Getting Started with Mock</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="#creating-a-mock-from-an-existing-object">Creating a Mock from an Existing Object</a></li> |
| </ul> |
| </li> |
| <li><a class="reference internal" href="#patch-decorators">Patch Decorators</a></li> |
| </ul> |
| </li> |
| </ul> |
| |
| <h4>Previous topic</h4> |
| <p class="topless"><a href="magicmock.html" |
| title="previous chapter">Mocking Magic Methods</a></p> |
| <h4>Next topic</h4> |
| <p class="topless"><a href="examples.html" |
| title="next chapter">Further Examples</a></p> |
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