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1.56 + <div class="section" id="getting-started-with-mock">
1.57 +<h1>Getting Started with Mock<a class="headerlink" href="#getting-started-with-mock" title="Permalink to this headline">¶</a></h1>
1.58 +<span class="target" id="getting-started"></span><span class="target" id="index-0"></span><div class="section" id="using-mock">
1.59 +<h2>Using Mock<a class="headerlink" href="#using-mock" title="Permalink to this headline">¶</a></h2>
1.60 +<div class="section" id="mock-patching-methods">
1.61 +<h3>Mock Patching Methods<a class="headerlink" href="#mock-patching-methods" title="Permalink to this headline">¶</a></h3>
1.62 +<p>Common uses for <tt class="xref py py-class docutils literal"><span class="pre">Mock</span></tt> objects include:</p>
1.63 +<ul class="simple">
1.64 +<li>Patching methods</li>
1.65 +<li>Recording method calls on objects</li>
1.66 +</ul>
1.67 +<p>You might want to replace a method on an object to check that
1.68 +it is called with the correct arguments by another part of the system:</p>
1.69 +<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>
1.70 +<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>
1.71 +<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>
1.72 +<span class="go"><MagicMock name='method()' id='...'></span>
1.73 +</pre></div>
1.74 +</div>
1.75 +<p>Once our mock has been used (<cite>real.method</cite> in this example) it has methods
1.76 +and attributes that allow you to make assertions about how it has been used.</p>
1.77 +<div class="admonition note">
1.78 +<p class="first admonition-title">Note</p>
1.79 +<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
1.80 +are interchangeable. As the <cite>MagicMock</cite> is the more capable class it makes
1.81 +a sensible one to use by default.</p>
1.82 +</div>
1.83 +<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
1.84 +<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
1.85 +<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
1.86 +the correct arguments.</p>
1.87 +<p>This example tests that calling <cite>ProductionClass().method</cite> results in a call to
1.88 +the <cite>something</cite> method:</p>
1.89 +<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>
1.90 +<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>
1.91 +<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>
1.92 +<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>
1.93 +<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>
1.94 +<span class="gp">... </span> <span class="k">pass</span>
1.95 +<span class="gp">...</span>
1.96 +<span class="gp">>>> </span><span class="n">real</span> <span class="o">=</span> <span class="n">ProductionClass</span><span class="p">()</span>
1.97 +<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>
1.98 +<span class="gp">>>> </span><span class="n">real</span><span class="o">.</span><span class="n">method</span><span class="p">()</span>
1.99 +<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>
1.100 +</pre></div>
1.101 +</div>
1.102 +</div>
1.103 +<div class="section" id="mock-for-method-calls-on-an-object">
1.104 +<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>
1.105 +<p>In the last example we patched a method directly on an object to check that it
1.106 +was called correctly. Another common use case is to pass an object into a
1.107 +method (or some part of the system under test) and then check that it is used
1.108 +in the correct way.</p>
1.109 +<p>The simple <cite>ProductionClass</cite> below has a <cite>closer</cite> method. If it is called with
1.110 +an object then it calls <cite>close</cite> on it.</p>
1.111 +<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>
1.112 +<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>
1.113 +<span class="gp">... </span> <span class="n">something</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
1.114 +<span class="gp">...</span>
1.115 +</pre></div>
1.116 +</div>
1.117 +<p>So to test it we need to pass in an object with a <cite>close</cite> method and check
1.118 +that it was called correctly.</p>
1.119 +<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>
1.120 +<span class="gp">>>> </span><span class="n">mock</span> <span class="o">=</span> <span class="n">Mock</span><span class="p">()</span>
1.121 +<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>
1.122 +<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>
1.123 +</pre></div>
1.124 +</div>
1.125 +<p>We don’t have to do any work to provide the ‘close’ method on our mock.
1.126 +Accessing close creates it. So, if ‘close’ hasn’t already been called then
1.127 +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>
1.128 +will raise a failure exception.</p>
1.129 +</div>
1.130 +<div class="section" id="mocking-classes">
1.131 +<h3>Mocking Classes<a class="headerlink" href="#mocking-classes" title="Permalink to this headline">¶</a></h3>
1.132 +<p>A common use case is to mock out classes instantiated by your code under test.
1.133 +When you patch a class, then that class is replaced with a mock. Instances
1.134 +are created by <em>calling the class</em>. This means you access the “mock instance”
1.135 +by looking at the return value of the mocked class.</p>
1.136 +<p>In the example below we have a function <cite>some_function</cite> that instantiates <cite>Foo</cite>
1.137 +and calls a method on it. The call to <cite>patch</cite> replaces the class <cite>Foo</cite> with a
1.138 +mock. The <cite>Foo</cite> instance is the result of calling the mock, so it is configured
1.139 +by modifying the mock <tt class="xref py py-attr docutils literal"><span class="pre">return_value</span></tt>.</p>
1.140 +<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>
1.141 +<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>
1.142 +<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>
1.143 +<span class="gp">...</span>
1.144 +<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>
1.145 +<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>
1.146 +<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>
1.147 +<span class="gp">... </span> <span class="n">result</span> <span class="o">=</span> <span class="n">some_function</span><span class="p">()</span>
1.148 +<span class="gp">... </span> <span class="k">assert</span> <span class="n">result</span> <span class="o">==</span> <span class="s">'the result'</span>
1.149 +</pre></div>
1.150 +</div>
1.151 +</div>
1.152 +<div class="section" id="naming-your-mocks">
1.153 +<h3>Naming your mocks<a class="headerlink" href="#naming-your-mocks" title="Permalink to this headline">¶</a></h3>
1.154 +<p>It can be useful to give your mocks a name. The name is shown in the repr of
1.155 +the mock and can be helpful when the mock appears in test failure messages. The
1.156 +name is also propagated to attributes or methods of the mock:</p>
1.157 +<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>
1.158 +<span class="gp">>>> </span><span class="n">mock</span>
1.159 +<span class="go"><MagicMock name='foo' id='...'></span>
1.160 +<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">method</span>
1.161 +<span class="go"><MagicMock name='foo.method' id='...'></span>
1.162 +</pre></div>
1.163 +</div>
1.164 +</div>
1.165 +<div class="section" id="tracking-all-calls">
1.166 +<h3>Tracking all Calls<a class="headerlink" href="#tracking-all-calls" title="Permalink to this headline">¶</a></h3>
1.167 +<p>Often you want to track more than a single call to a method. The
1.168 +<tt class="xref py py-attr docutils literal"><span class="pre">mock_calls</span></tt> attribute records all calls
1.169 +to child attributes of the mock - and also to their children.</p>
1.170 +<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>
1.171 +<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">method</span><span class="p">()</span>
1.172 +<span class="go"><MagicMock name='mock.method()' id='...'></span>
1.173 +<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>
1.174 +<span class="go"><MagicMock name='mock.attribute.method()' id='...'></span>
1.175 +<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">mock_calls</span>
1.176 +<span class="go">[call.method(), call.attribute.method(10, x=53)]</span>
1.177 +</pre></div>
1.178 +</div>
1.179 +<p>If you make an assertion about <cite>mock_calls</cite> and any unexpected methods
1.180 +have been called, then the assertion will fail. This is useful because as well
1.181 +as asserting that the calls you expected have been made, you are also checking
1.182 +that they were made in the right order and with no additional calls:</p>
1.183 +<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
1.184 +<cite>mock_calls</cite>:</p>
1.185 +<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>
1.186 +<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>
1.187 +<span class="go">True</span>
1.188 +</pre></div>
1.189 +</div>
1.190 +</div>
1.191 +<div class="section" id="setting-return-values-and-attributes">
1.192 +<h3>Setting Return Values and Attributes<a class="headerlink" href="#setting-return-values-and-attributes" title="Permalink to this headline">¶</a></h3>
1.193 +<p>Setting the return values on a mock object is trivially easy:</p>
1.194 +<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>
1.195 +<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>
1.196 +<span class="gp">>>> </span><span class="n">mock</span><span class="p">()</span>
1.197 +<span class="go">3</span>
1.198 +</pre></div>
1.199 +</div>
1.200 +<p>Of course you can do the same for methods on the mock:</p>
1.201 +<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>
1.202 +<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>
1.203 +<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">method</span><span class="p">()</span>
1.204 +<span class="go">3</span>
1.205 +</pre></div>
1.206 +</div>
1.207 +<p>The return value can also be set in the constructor:</p>
1.208 +<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>
1.209 +<span class="gp">>>> </span><span class="n">mock</span><span class="p">()</span>
1.210 +<span class="go">3</span>
1.211 +</pre></div>
1.212 +</div>
1.213 +<p>If you need an attribute setting on your mock, just do it:</p>
1.214 +<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>
1.215 +<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>
1.216 +<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">x</span>
1.217 +<span class="go">3</span>
1.218 +</pre></div>
1.219 +</div>
1.220 +<p>Sometimes you want to mock up a more complex situation, like for example
1.221 +<cite>mock.connection.cursor().execute(“SELECT 1”)</cite>. If we wanted this call to
1.222 +return a list, then we have to configure the result of the nested call.</p>
1.223 +<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
1.224 +this for easy assertion afterwards:</p>
1.225 +<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>
1.226 +<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>
1.227 +<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>
1.228 +<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>
1.229 +<span class="go">['foo']</span>
1.230 +<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>
1.231 +<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">mock_calls</span>
1.232 +<span class="go">[call.connection.cursor(), call.connection.cursor().execute('SELECT 1')]</span>
1.233 +<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>
1.234 +<span class="go">True</span>
1.235 +</pre></div>
1.236 +</div>
1.237 +<p>It is the call to <cite>.call_list()</cite> that turns our call object into a list of
1.238 +calls representing the chained calls.</p>
1.239 +</div>
1.240 +<div class="section" id="raising-exceptions-with-mocks">
1.241 +<h3>Raising exceptions with mocks<a class="headerlink" href="#raising-exceptions-with-mocks" title="Permalink to this headline">¶</a></h3>
1.242 +<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
1.243 +exception class or instance then the exception will be raised when the mock
1.244 +is called.</p>
1.245 +<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>
1.246 +<span class="gp">>>> </span><span class="n">mock</span><span class="p">()</span>
1.247 +<span class="gt">Traceback (most recent call last):</span>
1.248 + <span class="c">...</span>
1.249 +<span class="gr">Exception</span>: <span class="n">Boom!</span>
1.250 +</pre></div>
1.251 +</div>
1.252 +</div>
1.253 +<div class="section" id="side-effect-functions-and-iterables">
1.254 +<h3>Side effect functions and iterables<a class="headerlink" href="#side-effect-functions-and-iterables" title="Permalink to this headline">¶</a></h3>
1.255 +<p><cite>side_effect</cite> can also be set to a function or an iterable. The use case for
1.256 +<cite>side_effect</cite> as an iterable is where your mock is going to be called several
1.257 +times, and you want each call to return a different value. When you set
1.258 +<cite>side_effect</cite> to an iterable every call to the mock returns the next value
1.259 +from the iterable:</p>
1.260 +<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>
1.261 +<span class="gp">>>> </span><span class="n">mock</span><span class="p">()</span>
1.262 +<span class="go">4</span>
1.263 +<span class="gp">>>> </span><span class="n">mock</span><span class="p">()</span>
1.264 +<span class="go">5</span>
1.265 +<span class="gp">>>> </span><span class="n">mock</span><span class="p">()</span>
1.266 +<span class="go">6</span>
1.267 +</pre></div>
1.268 +</div>
1.269 +<p>For more advanced use cases, like dynamically varying the return values
1.270 +depending on what the mock is called with, <cite>side_effect</cite> can be a function.
1.271 +The function will be called with the same arguments as the mock. Whatever the
1.272 +function returns is what the call returns:</p>
1.273 +<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>
1.274 +<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>
1.275 +<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>
1.276 +<span class="gp">...</span>
1.277 +<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>
1.278 +<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>
1.279 +<span class="go">1</span>
1.280 +<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>
1.281 +<span class="go">2</span>
1.282 +</pre></div>
1.283 +</div>
1.284 +</div>
1.285 +<div class="section" id="creating-a-mock-from-an-existing-object">
1.286 +<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>
1.287 +<p>One problem with over use of mocking is that it couples your tests to the
1.288 +implementation of your mocks rather than your real code. Suppose you have a
1.289 +class that implements <cite>some_method</cite>. In a test for another class, you
1.290 +provide a mock of this object that <em>also</em> provides <cite>some_method</cite>. If later
1.291 +you refactor the first class, so that it no longer has <cite>some_method</cite> - then
1.292 +your tests will continue to pass even though your code is now broken!</p>
1.293 +<p><cite>Mock</cite> allows you to provide an object as a specification for the mock,
1.294 +using the <cite>spec</cite> keyword argument. Accessing methods / attributes on the
1.295 +mock that don’t exist on your specification object will immediately raise an
1.296 +attribute error. If you change the implementation of your specification, then
1.297 +tests that use that class will start failing immediately without you having to
1.298 +instantiate the class in those tests.</p>
1.299 +<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>
1.300 +<span class="gp">>>> </span><span class="n">mock</span><span class="o">.</span><span class="n">old_method</span><span class="p">()</span>
1.301 +<span class="gt">Traceback (most recent call last):</span>
1.302 + <span class="c">...</span>
1.303 +<span class="gr">AttributeError</span>: <span class="n">object has no attribute 'old_method'</span>
1.304 +</pre></div>
1.305 +</div>
1.306 +<p>If you want a stronger form of specification that prevents the setting
1.307 +of arbitrary attributes as well as the getting of them then you can use
1.308 +<cite>spec_set</cite> instead of <cite>spec</cite>.</p>
1.309 +</div>
1.310 +</div>
1.311 +<div class="section" id="patch-decorators">
1.312 +<h2>Patch Decorators<a class="headerlink" href="#patch-decorators" title="Permalink to this headline">¶</a></h2>
1.313 +<div class="admonition note">
1.314 +<p class="first admonition-title">Note</p>
1.315 +<p class="last">With <cite>patch</cite> it matters that you patch objects in the namespace where they
1.316 +are looked up. This is normally straightforward, but for a quick guide
1.317 +read <a class="reference internal" href="patch.html#where-to-patch"><em>where to patch</em></a>.</p>
1.318 +</div>
1.319 +<p>A common need in tests is to patch a class attribute or a module attribute,
1.320 +for example patching a builtin or patching a class in a module to test that it
1.321 +is instantiated. Modules and classes are effectively global, so patching on
1.322 +them has to be undone after the test or the patch will persist into other
1.323 +tests and cause hard to diagnose problems.</p>
1.324 +<p>mock provides three convenient decorators for this: <cite>patch</cite>, <cite>patch.object</cite> and
1.325 +<cite>patch.dict</cite>. <cite>patch</cite> takes a single string, of the form
1.326 +<cite>package.module.Class.attribute</cite> to specify the attribute you are patching. It
1.327 +also optionally takes a value that you want the attribute (or class or
1.328 +whatever) to be replaced with. ‘patch.object’ takes an object and the name of
1.329 +the attribute you would like patched, plus optionally the value to patch it
1.330 +with.</p>
1.331 +<p><cite>patch.object</cite>:</p>
1.332 +<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>
1.333 +<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>
1.334 +<span class="gp">... </span><span class="k">def</span> <span class="nf">test</span><span class="p">():</span>
1.335 +<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>
1.336 +<span class="gp">...</span>
1.337 +<span class="gp">>>> </span><span class="n">test</span><span class="p">()</span>
1.338 +<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>
1.339 +
1.340 +<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>
1.341 +<span class="gp">... </span><span class="k">def</span> <span class="nf">test</span><span class="p">():</span>
1.342 +<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>
1.343 +<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>
1.344 +<span class="gp">...</span>
1.345 +<span class="gp">>>> </span><span class="n">test</span><span class="p">()</span>
1.346 +</pre></div>
1.347 +</div>
1.348 +<p>If you are patching a module (including <cite>__builtin__</cite>) then use <cite>patch</cite>
1.349 +instead of <cite>patch.object</cite>:</p>
1.350 +<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>
1.351 +<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>
1.352 +<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>
1.353 +<span class="gp">...</span>
1.354 +<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>
1.355 +<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>
1.356 +</pre></div>
1.357 +</div>
1.358 +<p>The module name can be ‘dotted’, in the form <cite>package.module</cite> if needed:</p>
1.359 +<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>
1.360 +<span class="gp">... </span><span class="k">def</span> <span class="nf">test</span><span class="p">():</span>
1.361 +<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>
1.362 +<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>
1.363 +<span class="gp">...</span>
1.364 +<span class="gp">>>> </span><span class="n">test</span><span class="p">()</span>
1.365 +</pre></div>
1.366 +</div>
1.367 +<p>A nice pattern is to actually decorate test methods themselves:</p>
1.368 +<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>
1.369 +<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>
1.370 +<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>
1.371 +<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>
1.372 +<span class="gp">...</span>
1.373 +<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>
1.374 +<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>
1.375 +<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>
1.376 +</pre></div>
1.377 +</div>
1.378 +<p>If you want to patch with a Mock, you can use <cite>patch</cite> with only one argument
1.379 +(or <cite>patch.object</cite> with two arguments). The mock will be created for you and
1.380 +passed into the test function / method:</p>
1.381 +<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>
1.382 +<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>
1.383 +<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>
1.384 +<span class="gp">... </span> <span class="n">SomeClass</span><span class="o">.</span><span class="n">static_method</span><span class="p">()</span>
1.385 +<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>
1.386 +<span class="gp">...</span>
1.387 +<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>
1.388 +</pre></div>
1.389 +</div>
1.390 +<p>You can stack up multiple patch decorators using this pattern:</p>
1.391 +<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>
1.392 +<span class="gp">... </span> <span class="nd">@patch</span><span class="p">(</span><span class="s">'package.module.ClassName1'</span><span class="p">)</span>
1.393 +<span class="gp">... </span> <span class="nd">@patch</span><span class="p">(</span><span class="s">'package.module.ClassName2'</span><span class="p">)</span>
1.394 +<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>
1.395 +<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>
1.396 +<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>
1.397 +<span class="gp">...</span>
1.398 +<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>
1.399 +</pre></div>
1.400 +</div>
1.401 +<p>When you nest patch decorators the mocks are passed in to the decorated
1.402 +function in the same order they applied (the normal <em>python</em> order that
1.403 +decorators are applied). This means from the bottom up, so in the example
1.404 +above the mock for <cite>test_module.ClassName2</cite> is passed in first.</p>
1.405 +<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
1.406 +during a scope and restoring the dictionary to its original state when the test
1.407 +ends:</p>
1.408 +<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>
1.409 +<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>
1.410 +<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>
1.411 +<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>
1.412 +<span class="gp">...</span>
1.413 +<span class="gp">>>> </span><span class="k">assert</span> <span class="n">foo</span> <span class="o">==</span> <span class="n">original</span>
1.414 +</pre></div>
1.415 +</div>
1.416 +<p><cite>patch</cite>, <cite>patch.object</cite> and <cite>patch.dict</cite> can all be used as context managers.</p>
1.417 +<p>Where you use <cite>patch</cite> to create a mock for you, you can get a reference to the
1.418 +mock using the “as” form of the with statement:</p>
1.419 +<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>
1.420 +<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>
1.421 +<span class="gp">... </span> <span class="k">pass</span>
1.422 +<span class="gp">...</span>
1.423 +<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>
1.424 +<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>
1.425 +<span class="gp">... </span> <span class="n">real</span> <span class="o">=</span> <span class="n">ProductionClass</span><span class="p">()</span>
1.426 +<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>
1.427 +<span class="gp">...</span>
1.428 +<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>
1.429 +</pre></div>
1.430 +</div>
1.431 +<p>As an alternative <cite>patch</cite>, <cite>patch.object</cite> and <cite>patch.dict</cite> can be used as
1.432 +class decorators. When used in this way it is the same as applying the
1.433 +decorator indvidually to every method whose name starts with “test”.</p>
1.434 +<p>For some more advanced examples, see the <a class="reference internal" href="examples.html#further-examples"><em>Further Examples</em></a> page.</p>
1.435 +</div>
1.436 +</div>
1.437 +
1.438 +
1.439 + </div>
1.440 + </div>
1.441 + </div>
1.442 + <div class="sphinxsidebar">
1.443 + <div class="sphinxsidebarwrapper">
1.444 + <h3><a href="index.html">Table Of Contents</a></h3>
1.445 + <ul>
1.446 +<li><a class="reference internal" href="#">Getting Started with Mock</a><ul>
1.447 +<li><a class="reference internal" href="#using-mock">Using Mock</a><ul>
1.448 +<li><a class="reference internal" href="#mock-patching-methods">Mock Patching Methods</a></li>
1.449 +<li><a class="reference internal" href="#mock-for-method-calls-on-an-object">Mock for Method Calls on an Object</a></li>
1.450 +<li><a class="reference internal" href="#mocking-classes">Mocking Classes</a></li>
1.451 +<li><a class="reference internal" href="#naming-your-mocks">Naming your mocks</a></li>
1.452 +<li><a class="reference internal" href="#tracking-all-calls">Tracking all Calls</a></li>
1.453 +<li><a class="reference internal" href="#setting-return-values-and-attributes">Setting Return Values and Attributes</a></li>
1.454 +<li><a class="reference internal" href="#raising-exceptions-with-mocks">Raising exceptions with mocks</a></li>
1.455 +<li><a class="reference internal" href="#side-effect-functions-and-iterables">Side effect functions and iterables</a></li>
1.456 +<li><a class="reference internal" href="#creating-a-mock-from-an-existing-object">Creating a Mock from an Existing Object</a></li>
1.457 +</ul>
1.458 +</li>
1.459 +<li><a class="reference internal" href="#patch-decorators">Patch Decorators</a></li>
1.460 +</ul>
1.461 +</li>
1.462 +</ul>
1.463 +
1.464 + <h4>Previous topic</h4>
1.465 + <p class="topless"><a href="magicmock.html"
1.466 + title="previous chapter">Mocking Magic Methods</a></p>
1.467 + <h4>Next topic</h4>
1.468 + <p class="topless"><a href="examples.html"
1.469 + title="next chapter">Further Examples</a></p>
1.470 + <h3>This Page</h3>
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1.508 + © Copyright 2007-2012, Michael Foord & the mock team.
1.509 + Last updated on Oct 07, 2012.
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