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<h3><a href="contents.html">Table Of Contents</a></h3>
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<li><a class="reference internal" href="#">Some Issues and Questions</a><ul>
<li><a class="reference internal" href="#on-naming-nosetests-licensing-and-magic">On naming, nosetests, licensing and magic</a><ul>
<li><a class="reference internal" href="#why-a-py-test-instead-of-a-pytest-command">Why a <tt class="docutils literal"><span class="pre">py.test</span></tt> instead of a <tt class="docutils literal"><span class="pre">pytest</span></tt> command?</a></li>
<li><a class="reference internal" href="#how-does-py-test-relate-to-nose-and-unittest">How does py.test relate to nose and unittest?</a></li>
<li><a class="reference internal" href="#what-s-this-magic-with-py-test">What’s this “magic” with py.test?</a></li>
</ul>
</li>
<li><a class="reference internal" href="#function-arguments-parametrized-tests-and-setup">Function arguments, parametrized tests and setup</a><ul>
<li><a class="reference internal" href="#is-using-funcarg-versus-xunit-setup-a-style-question">Is using funcarg- versus xUnit setup a style question?</a></li>
<li><a class="reference internal" href="#why-the-pytest-funcarg-name-for-funcarg-factories">Why the <tt class="docutils literal"><span class="pre">pytest_funcarg__*</span></tt> name for funcarg factories?</a></li>
<li><a class="reference internal" href="#can-i-yield-multiple-values-from-a-funcarg-factory-function">Can I yield multiple values from a funcarg factory function?</a></li>
</ul>
</li>
<li><a class="reference internal" href="#py-test-interaction-with-other-packages">py.test interaction with other packages</a><ul>
<li><a class="reference internal" href="#issues-with-py-test-multiprocess-and-setuptools">Issues with py.test, multiprocess and setuptools?</a></li>
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<div class="section" id="some-issues-and-questions">
<h1>Some Issues and Questions<a class="headerlink" href="#some-issues-and-questions" title="Permalink to this headline">¶</a></h1>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">If you don’t find an answer here, checkout the <a class="reference internal" href="contact.html#contact-channels"><em>Contact channels</em></a>
to get help.</p>
</div>
<div class="section" id="on-naming-nosetests-licensing-and-magic">
<h2>On naming, nosetests, licensing and magic<a class="headerlink" href="#on-naming-nosetests-licensing-and-magic" title="Permalink to this headline">¶</a></h2>
<div class="section" id="why-a-py-test-instead-of-a-pytest-command">
<h3>Why a <tt class="docutils literal"><span class="pre">py.test</span></tt> instead of a <tt class="docutils literal"><span class="pre">pytest</span></tt> command?<a class="headerlink" href="#why-a-py-test-instead-of-a-pytest-command" title="Permalink to this headline">¶</a></h3>
<p>Some of the reasons are historic, others are practical. <tt class="docutils literal"><span class="pre">py.test</span></tt>
used to be part of the <tt class="docutils literal"><span class="pre">py</span></tt> package which provided several developer
utilities, all starting with <tt class="docutils literal"><span class="pre">py.<TAB></span></tt>, thus providing nice
TAB-completion. If
you install <tt class="docutils literal"><span class="pre">pip</span> <span class="pre">install</span> <span class="pre">pycmd</span></tt> you get these tools from a separate
package. These days the command line tool could be called <tt class="docutils literal"><span class="pre">pytest</span></tt>
but since many people have gotten used to the old name and there
is another tool named “pytest” we just decided to stick with
<tt class="docutils literal"><span class="pre">py.test</span></tt>.</p>
</div>
<div class="section" id="how-does-py-test-relate-to-nose-and-unittest">
<h3>How does py.test relate to nose and unittest?<a class="headerlink" href="#how-does-py-test-relate-to-nose-and-unittest" title="Permalink to this headline">¶</a></h3>
<p>py.test and <a class="reference external" href="http://somethingaboutorange.com/mrl/projects/nose/">nose</a> share basic philosophy when it comes
to running and writing Python tests. In fact, you can run many tests
written for nose with py.test. <a class="reference external" href="http://somethingaboutorange.com/mrl/projects/nose/">nose</a> was originally created
as a clone of <tt class="docutils literal"><span class="pre">py.test</span></tt> when py.test was in the <tt class="docutils literal"><span class="pre">0.8</span></tt> release
cycle. Note that starting with pytest-2.0 support for running unittest
test suites is majorly improved and you should be able to run
many Django and Twisted test suites without modification.</p>
</div>
<div class="section" id="what-s-this-magic-with-py-test">
<h3>What’s this “magic” with py.test?<a class="headerlink" href="#what-s-this-magic-with-py-test" title="Permalink to this headline">¶</a></h3>
<p>Around 2007 (version <tt class="docutils literal"><span class="pre">0.8</span></tt>) some people claimed that py.test
was using too much “magic”. Partly this has been fixed by removing
unused, deprecated or complicated code. It is today probably one
of the smallest, most universally runnable and most
customizable testing frameworks for Python. However,
<tt class="docutils literal"><span class="pre">py.test</span></tt> still uses many metaprogramming techniques and
reading its source is thus likely not something for Python beginners.</p>
<p>A second “magic” issue is arguably the assert statement debugging feature. When
loading test modules py.test rewrites the source code of assert statements. When
a rewritten assert statement fails, its error message has more information than
the original. py.test also has a second assert debugging technique. When an
<tt class="docutils literal"><span class="pre">assert</span></tt> statement that was missed by the rewriter fails, py.test
re-interprets the expression to show intermediate values if a test fails. This
second technique suffers from a caveat that the rewriting does not: If your
expression has side effects (better to avoid them anyway!) the intermediate
values may not be the same, confusing the reinterpreter and obfuscating the
initial error (this is also explained at the command line if it happens).
You can turn off all assertion debugging with <tt class="docutils literal"><span class="pre">py.test</span> <span class="pre">--assertmode=off</span></tt>.</p>
</div>
</div>
<div class="section" id="function-arguments-parametrized-tests-and-setup">
<h2>Function arguments, parametrized tests and setup<a class="headerlink" href="#function-arguments-parametrized-tests-and-setup" title="Permalink to this headline">¶</a></h2>
<div class="section" id="is-using-funcarg-versus-xunit-setup-a-style-question">
<h3>Is using funcarg- versus xUnit setup a style question?<a class="headerlink" href="#is-using-funcarg-versus-xunit-setup-a-style-question" title="Permalink to this headline">¶</a></h3>
<p>For simple applications and for people experienced with <a class="reference external" href="http://somethingaboutorange.com/mrl/projects/nose/">nose</a> or
unittest-style test setup using <a class="reference external" href="xunit_setup.html">xUnit style setup</a> probably
feels natural. For larger test suites, parametrized testing
or setup of complex test resources using <a class="reference external" href="test/funcargs.html">funcargs</a> may feel more natural.
Moreover, funcargs are ideal for writing advanced test support
code (like e.g. the <a class="reference external" href="test/plugin/monkeypatch.html">monkeypatch</a>, the <a class="reference external" href="test/plugin/tmpdir.html">tmpdir</a> or <a class="reference external" href="test/plugin/capture.html">capture</a> funcargs)
because the support code can register setup/teardown functions
in a managed class/module/function scope.</p>
</div>
<div class="section" id="why-the-pytest-funcarg-name-for-funcarg-factories">
<span id="why-pytest-pyfuncarg-methods"></span><h3>Why the <tt class="docutils literal"><span class="pre">pytest_funcarg__*</span></tt> name for funcarg factories?<a class="headerlink" href="#why-the-pytest-funcarg-name-for-funcarg-factories" title="Permalink to this headline">¶</a></h3>
<p>We like <a class="reference external" href="http://en.wikipedia.org/wiki/Convention_over_Configuration">Convention over Configuration</a> and didn’t see much point
in allowing a more flexible or abstract mechanism. Moreover,
it is nice to be able to search for <tt class="docutils literal"><span class="pre">pytest_funcarg__MYARG</span></tt> in
source code and safely find all factory functions for
the <tt class="docutils literal"><span class="pre">MYARG</span></tt> function argument.</p>
</div>
<div class="section" id="can-i-yield-multiple-values-from-a-funcarg-factory-function">
<h3>Can I yield multiple values from a funcarg factory function?<a class="headerlink" href="#can-i-yield-multiple-values-from-a-funcarg-factory-function" title="Permalink to this headline">¶</a></h3>
<p>There are two conceptual reasons why yielding from a factory function
is not possible:</p>
<ul class="simple">
<li>Calling factories for obtaining test function arguments
is part of setting up and running a test. At that
point it is not possible to add new test calls to
the test collection anymore.</li>
<li>If multiple factories yielded values there would
be no natural place to determine the combination
policy - in real-world examples some combinations
often should not run.</li>
</ul>
<p>Use the <a class="reference external" href="test/funcargs.html#parametrizing-tests">pytest_generate_tests</a> hook to solve both issues
and implement the <a class="reference external" href="http://tetamap.wordpress.com/2009/05/13/parametrizing-python-tests-generalized/">parametrization scheme of your choice</a>.</p>
</div>
</div>
<div class="section" id="py-test-interaction-with-other-packages">
<h2>py.test interaction with other packages<a class="headerlink" href="#py-test-interaction-with-other-packages" title="Permalink to this headline">¶</a></h2>
<div class="section" id="issues-with-py-test-multiprocess-and-setuptools">
<h3>Issues with py.test, multiprocess and setuptools?<a class="headerlink" href="#issues-with-py-test-multiprocess-and-setuptools" title="Permalink to this headline">¶</a></h3>
<p>On windows the multiprocess package will instantiate sub processes
by pickling and thus implicitly re-import a lot of local modules.
Unfortunately, setuptools-0.6.11 does not <tt class="docutils literal"><span class="pre">if</span> <span class="pre">__name__=='__main__'</span></tt>
protect its generated command line script. This leads to infinite
recursion when running a test that instantiates Processes.</p>
<p>A good solution is to <a class="reference external" href="http://pypi.python.org/pypi/distribute#installation-instructions">install Distribute</a> as a drop-in replacement
for setuptools and then re-install <tt class="docutils literal"><span class="pre">pytest</span></tt>. Otherwise you could
fix the script that is created by setuptools by inserting an
<tt class="docutils literal"><span class="pre">if</span> <span class="pre">__name__</span> <span class="pre">==</span> <span class="pre">'__main__'</span></tt>. Or you can create a “pytest.py”
script with this content and invoke that with the python version:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">pytest</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">'__main__'</span><span class="p">:</span>
<span class="n">pytest</span><span class="o">.</span><span class="n">main</span><span class="p">()</span>
</pre></div>
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