<!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 <tt class="xref py py-meth docutils literal"><span class="pre">monkeypatch.setattr()</span></tt> 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>
<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.
Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
</div>
<script type="text/javascript">
var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-7597274-13']);
_gaq.push(['_trackPageview']);
(function() {
var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
})();
</script>
<script type="text/javascript" src="https://apis.google.com/js/plusone.js"></script>
</body>
</html>
