<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Monkeypatching/mocking modules and environments</title> <link rel="stylesheet" href="_static/sphinxdoc.css" type="text/css" /> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '', VERSION: '2.3.4.1', COLLAPSE_INDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </script> <script type="text/javascript" src="_static/jquery.js"></script> <script type="text/javascript" src="_static/underscore.js"></script> <script type="text/javascript" src="_static/doctools.js"></script> <link rel="top" title="None" href="index.html" /> <link rel="up" title="py.test reference documentation" href="apiref.html" /> <link rel="next" title="xdist: pytest distributed testing plugin" href="xdist.html" /> <link rel="prev" title="Capturing of the stdout/stderr output" href="capture.html" /> </head> <body> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="xdist.html" title="xdist: pytest distributed testing plugin" accesskey="N">next</a></li> <li class="right" > <a href="capture.html" title="Capturing of the stdout/stderr output" accesskey="P">previous</a> |</li> <li><a href="contents.html">pytest-2.3.4.1</a> »</li> <li><a href="apiref.html" accesskey="U">py.test reference documentation</a> »</li> <g:plusone></g:plusone> </ul> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <div id="searchbox" style="display: none"> <form class="search" action="search.html" method="get"> <input type="text" name="q" size="18" /> <input type="submit" value="Search" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('#searchbox').show(0);</script> <h3>quicklinks</h3> <div style="text-align: left; font-size: 100%; vertical-align: middle;"> <table> <tr> <td> <a href="index.html">home</a> </td><td> <a href="contents.html">TOC/contents</a> </td></tr><tr><td> <a href="getting-started.html">install</a> </td><td> <a href="changelog.html">changelog</a> </td></tr><tr><td> <a href="example/index.html">examples</a> </td><td> <a href="customize.html">customize</a> </td></tr><tr><td> <a href="https://bitbucket.org/hpk42/pytest/issues?status=new&status=open">issues[bb]</a> </td><td> <a href="contact.html">contact</a> </td></tr></table> </div> <h3><a href="contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">Monkeypatching/mocking modules and environments</a><ul> <li><a class="reference internal" href="#simple-example-monkeypatching-functions">Simple example: monkeypatching functions</a></li> <li><a class="reference internal" href="#method-reference-of-the-monkeypatch-function-argument">Method reference of the monkeypatch function argument</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="capture.html" title="previous chapter">Capturing of the stdout/stderr output</a></p> <h4>Next topic</h4> <p class="topless"><a href="xdist.html" title="next chapter">xdist: pytest distributed testing plugin</a></p> </div> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="monkeypatching-mocking-modules-and-environments"> <h1>Monkeypatching/mocking modules and environments<a class="headerlink" href="#monkeypatching-mocking-modules-and-environments" title="Permalink to this headline">¶</a></h1> <p>Sometimes tests need to invoke functionality which depends on global settings or which invokes code which cannot be easily tested such as network access. The <tt class="docutils literal"><span class="pre">monkeypatch</span></tt> function argument helps you to safely set/delete an attribute, dictionary item or environment variable or to modify <tt class="docutils literal"><span class="pre">sys.path</span></tt> for importing. See the <a class="reference external" href="http://tetamap.wordpress.com/2009/03/03/monkeypatching-in-unit-tests-done-right/">monkeypatch blog post</a> for some introduction material and a discussion of its motivation.</p> <div class="section" id="simple-example-monkeypatching-functions"> <h2>Simple example: monkeypatching functions<a class="headerlink" href="#simple-example-monkeypatching-functions" title="Permalink to this headline">¶</a></h2> <p>If you want to pretend that <tt class="docutils literal"><span class="pre">os.expanduser</span></tt> returns a certain directory, you can use the <a class="reference internal" href="#_pytest.monkeypatch.monkeypatch.setattr" title="_pytest.monkeypatch.monkeypatch.setattr"><tt class="xref py py-meth docutils literal"><span class="pre">monkeypatch.setattr()</span></tt></a> method to patch this function before calling into a function which uses it:</p> <div class="highlight-python"><div class="highlight"><pre><span class="c"># content of test_module.py</span> <span class="kn">import</span> <span class="nn">os.path</span> <span class="k">def</span> <span class="nf">getssh</span><span class="p">():</span> <span class="c"># pseudo application code</span> <span class="k">return</span> <span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">expanduser</span><span class="p">(</span><span class="s">"~admin"</span><span class="p">),</span> <span class="s">'.ssh'</span><span class="p">)</span> <span class="k">def</span> <span class="nf">test_mytest</span><span class="p">(</span><span class="n">monkeypatch</span><span class="p">):</span> <span class="k">def</span> <span class="nf">mockreturn</span><span class="p">(</span><span class="n">path</span><span class="p">):</span> <span class="k">return</span> <span class="s">'/abc'</span> <span class="n">monkeypatch</span><span class="o">.</span><span class="n">setattr</span><span class="p">(</span><span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="p">,</span> <span class="s">'expanduser'</span><span class="p">,</span> <span class="n">mockreturn</span><span class="p">)</span> <span class="n">x</span> <span class="o">=</span> <span class="n">getssh</span><span class="p">()</span> <span class="k">assert</span> <span class="n">x</span> <span class="o">==</span> <span class="s">'/abc/.ssh'</span> </pre></div> </div> <p>Here our test function monkeypatches <tt class="docutils literal"><span class="pre">os.path.expanduser</span></tt> and then calls into an function that calls it. After the test function finishes the <tt class="docutils literal"><span class="pre">os.path.expanduser</span></tt> modification will be undone.</p> </div> <div class="section" id="method-reference-of-the-monkeypatch-function-argument"> <h2>Method reference of the monkeypatch function argument<a class="headerlink" href="#method-reference-of-the-monkeypatch-function-argument" title="Permalink to this headline">¶</a></h2> <dl class="class"> <dt id="_pytest.monkeypatch.monkeypatch"> <em class="property">class </em><tt class="descname">monkeypatch</tt><a class="reference internal" href="_modules/_pytest/monkeypatch.html#monkeypatch"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.monkeypatch.monkeypatch" title="Permalink to this definition">¶</a></dt> <dd><p>object keeping a record of setattr/item/env/syspath changes.</p> <dl class="method"> <dt id="_pytest.monkeypatch.monkeypatch.setattr"> <tt class="descname">setattr</tt><big>(</big><em>obj</em>, <em>name</em>, <em>value</em>, <em>raising=True</em><big>)</big><a class="reference internal" href="_modules/_pytest/monkeypatch.html#monkeypatch.setattr"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.monkeypatch.monkeypatch.setattr" title="Permalink to this definition">¶</a></dt> <dd><p>set attribute <tt class="docutils literal"><span class="pre">name</span></tt> on <tt class="docutils literal"><span class="pre">obj</span></tt> to <tt class="docutils literal"><span class="pre">value</span></tt>, by default raise AttributeEror if the attribute did not exist.</p> </dd></dl> <dl class="method"> <dt id="_pytest.monkeypatch.monkeypatch.delattr"> <tt class="descname">delattr</tt><big>(</big><em>obj</em>, <em>name</em>, <em>raising=True</em><big>)</big><a class="reference internal" href="_modules/_pytest/monkeypatch.html#monkeypatch.delattr"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.monkeypatch.monkeypatch.delattr" title="Permalink to this definition">¶</a></dt> <dd><p>delete attribute <tt class="docutils literal"><span class="pre">name</span></tt> from <tt class="docutils literal"><span class="pre">obj</span></tt>, by default raise AttributeError it the attribute did not previously exist.</p> </dd></dl> <dl class="method"> <dt id="_pytest.monkeypatch.monkeypatch.setitem"> <tt class="descname">setitem</tt><big>(</big><em>dic</em>, <em>name</em>, <em>value</em><big>)</big><a class="reference internal" href="_modules/_pytest/monkeypatch.html#monkeypatch.setitem"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.monkeypatch.monkeypatch.setitem" title="Permalink to this definition">¶</a></dt> <dd><p>set dictionary entry <tt class="docutils literal"><span class="pre">name</span></tt> to value.</p> </dd></dl> <dl class="method"> <dt id="_pytest.monkeypatch.monkeypatch.delitem"> <tt class="descname">delitem</tt><big>(</big><em>dic</em>, <em>name</em>, <em>raising=True</em><big>)</big><a class="reference internal" href="_modules/_pytest/monkeypatch.html#monkeypatch.delitem"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.monkeypatch.monkeypatch.delitem" title="Permalink to this definition">¶</a></dt> <dd><p>delete <tt class="docutils literal"><span class="pre">name</span></tt> from dict, raise KeyError if it doesn’t exist.</p> </dd></dl> <dl class="method"> <dt id="_pytest.monkeypatch.monkeypatch.setenv"> <tt class="descname">setenv</tt><big>(</big><em>name</em>, <em>value</em>, <em>prepend=None</em><big>)</big><a class="reference internal" href="_modules/_pytest/monkeypatch.html#monkeypatch.setenv"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.monkeypatch.monkeypatch.setenv" title="Permalink to this definition">¶</a></dt> <dd><p>set environment variable <tt class="docutils literal"><span class="pre">name</span></tt> to <tt class="docutils literal"><span class="pre">value</span></tt>. if <tt class="docutils literal"><span class="pre">prepend</span></tt> is a character, read the current environment variable value and prepend the <tt class="docutils literal"><span class="pre">value</span></tt> adjoined with the <tt class="docutils literal"><span class="pre">prepend</span></tt> character.</p> </dd></dl> <dl class="method"> <dt id="_pytest.monkeypatch.monkeypatch.delenv"> <tt class="descname">delenv</tt><big>(</big><em>name</em>, <em>raising=True</em><big>)</big><a class="reference internal" href="_modules/_pytest/monkeypatch.html#monkeypatch.delenv"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.monkeypatch.monkeypatch.delenv" title="Permalink to this definition">¶</a></dt> <dd><p>delete <tt class="docutils literal"><span class="pre">name</span></tt> from environment, raise KeyError it not exists.</p> </dd></dl> <dl class="method"> <dt id="_pytest.monkeypatch.monkeypatch.syspath_prepend"> <tt class="descname">syspath_prepend</tt><big>(</big><em>path</em><big>)</big><a class="reference internal" href="_modules/_pytest/monkeypatch.html#monkeypatch.syspath_prepend"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.monkeypatch.monkeypatch.syspath_prepend" title="Permalink to this definition">¶</a></dt> <dd><p>prepend <tt class="docutils literal"><span class="pre">path</span></tt> to <tt class="docutils literal"><span class="pre">sys.path</span></tt> list of import locations.</p> </dd></dl> <dl class="method"> <dt id="_pytest.monkeypatch.monkeypatch.chdir"> <tt class="descname">chdir</tt><big>(</big><em>path</em><big>)</big><a class="reference internal" href="_modules/_pytest/monkeypatch.html#monkeypatch.chdir"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.monkeypatch.monkeypatch.chdir" title="Permalink to this definition">¶</a></dt> <dd><p>change the current working directory to the specified path path can be a string or a py.path.local object</p> </dd></dl> <dl class="method"> <dt id="_pytest.monkeypatch.monkeypatch.undo"> <tt class="descname">undo</tt><big>(</big><big>)</big><a class="reference internal" href="_modules/_pytest/monkeypatch.html#monkeypatch.undo"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.monkeypatch.monkeypatch.undo" title="Permalink to this definition">¶</a></dt> <dd><p>undo previous changes. This call consumes the undo stack. Calling it a second time has no effect unless you do more monkeypatching after the undo call.</p> </dd></dl> </dd></dl> <p><tt class="docutils literal"><span class="pre">monkeypatch.setattr/delattr/delitem/delenv()</span></tt> all by default raise an Exception if the target does not exist. Pass <tt class="docutils literal"><span class="pre">raising=False</span></tt> if you want to skip this check.</p> </div> </div> </div> </div> </div> <div class="clearer"></div> </div> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="xdist.html" title="xdist: pytest distributed testing plugin" >next</a></li> <li class="right" > <a href="capture.html" title="Capturing of the stdout/stderr output" >previous</a> |</li> <li><a href="contents.html">pytest-2.3.4.1</a> »</li> <li><a href="apiref.html" >py.test reference documentation</a> »</li> <g:plusone></g:plusone> </ul> </div> <div class="footer"> © Copyright 2012, holger krekel. 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