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<div class="section" id="module-test">
<span id="test-regression-tests-package-for-python"></span><h1>25.5. <a class="reference internal" href="#module-test" title="test: Regression tests package containing the testing suite for Python."><tt class="xref py py-mod docutils literal"><span class="pre">test</span></tt></a> — Regression tests package for Python<a class="headerlink" href="#module-test" title="Permalink to this headline">¶</a></h1>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The <a class="reference internal" href="#module-test" title="test: Regression tests package containing the testing suite for Python."><tt class="xref py py-mod docutils literal"><span class="pre">test</span></tt></a> package is meant for internal use by Python only. It is
documented for the benefit of the core developers of Python. Any use of
this package outside of Python’s standard library is discouraged as code
mentioned here can change or be removed without notice between releases of
Python.</p>
</div>
<p>The <a class="reference internal" href="#module-test" title="test: Regression tests package containing the testing suite for Python."><tt class="xref py py-mod docutils literal"><span class="pre">test</span></tt></a> package contains all regression tests for Python as well as the
modules <a class="reference internal" href="#module-test.support" title="test.support: Support for Python's regression test suite."><tt class="xref py py-mod docutils literal"><span class="pre">test.support</span></tt></a> and <tt class="xref py py-mod docutils literal"><span class="pre">test.regrtest</span></tt>.
<a class="reference internal" href="#module-test.support" title="test.support: Support for Python's regression test suite."><tt class="xref py py-mod docutils literal"><span class="pre">test.support</span></tt></a> is used to enhance your tests while
<tt class="xref py py-mod docutils literal"><span class="pre">test.regrtest</span></tt> drives the testing suite.</p>
<p>Each module in the <a class="reference internal" href="#module-test" title="test: Regression tests package containing the testing suite for Python."><tt class="xref py py-mod docutils literal"><span class="pre">test</span></tt></a> package whose name starts with <tt class="docutils literal"><span class="pre">test_</span></tt> is a
testing suite for a specific module or feature. All new tests should be written
using the <a class="reference internal" href="unittest.html#module-unittest" title="unittest: Unit testing framework for Python."><tt class="xref py py-mod docutils literal"><span class="pre">unittest</span></tt></a> or <a class="reference internal" href="doctest.html#module-doctest" title="doctest: Test pieces of code within docstrings."><tt class="xref py py-mod docutils literal"><span class="pre">doctest</span></tt></a> module. Some older tests are
written using a “traditional” testing style that compares output printed to
<tt class="docutils literal"><span class="pre">sys.stdout</span></tt>; this style of test is considered deprecated.</p>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt>Module <a class="reference internal" href="unittest.html#module-unittest" title="unittest: Unit testing framework for Python."><tt class="xref py py-mod docutils literal"><span class="pre">unittest</span></tt></a></dt>
<dd>Writing PyUnit regression tests.</dd>
<dt>Module <a class="reference internal" href="doctest.html#module-doctest" title="doctest: Test pieces of code within docstrings."><tt class="xref py py-mod docutils literal"><span class="pre">doctest</span></tt></a></dt>
<dd>Tests embedded in documentation strings.</dd>
</dl>
</div>
<div class="section" id="writing-unit-tests-for-the-test-package">
<span id="writing-tests"></span><h2>25.5.1. Writing Unit Tests for the <a class="reference internal" href="#module-test" title="test: Regression tests package containing the testing suite for Python."><tt class="xref py py-mod docutils literal"><span class="pre">test</span></tt></a> package<a class="headerlink" href="#writing-unit-tests-for-the-test-package" title="Permalink to this headline">¶</a></h2>
<p>It is preferred that tests that use the <a class="reference internal" href="unittest.html#module-unittest" title="unittest: Unit testing framework for Python."><tt class="xref py py-mod docutils literal"><span class="pre">unittest</span></tt></a> module follow a few
guidelines. One is to name the test module by starting it with <tt class="docutils literal"><span class="pre">test_</span></tt> and end
it with the name of the module being tested. The test methods in the test module
should start with <tt class="docutils literal"><span class="pre">test_</span></tt> and end with a description of what the method is
testing. This is needed so that the methods are recognized by the test driver as
test methods. Also, no documentation string for the method should be included. A
comment (such as <tt class="docutils literal"><span class="pre">#</span> <span class="pre">Tests</span> <span class="pre">function</span> <span class="pre">returns</span> <span class="pre">only</span> <span class="pre">True</span> <span class="pre">or</span> <span class="pre">False</span></tt>) should be used
to provide documentation for test methods. This is done because documentation
strings get printed out if they exist and thus what test is being run is not
stated.</p>
<p>A basic boilerplate is often used:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">unittest</span>
<span class="kn">from</span> <span class="nn">test</span> <span class="k">import</span> <span class="n">support</span>
<span class="k">class</span> <span class="nc">MyTestCase1</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>
<span class="c"># Only use setUp() and tearDown() if necessary</span>
<span class="k">def</span> <span class="nf">setUp</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="o">...</span> <span class="n">code</span> <span class="n">to</span> <span class="n">execute</span> <span class="ow">in</span> <span class="n">preparation</span> <span class="k">for</span> <span class="n">tests</span> <span class="o">...</span>
<span class="k">def</span> <span class="nf">tearDown</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="o">...</span> <span class="n">code</span> <span class="n">to</span> <span class="n">execute</span> <span class="n">to</span> <span class="n">clean</span> <span class="n">up</span> <span class="n">after</span> <span class="n">tests</span> <span class="o">...</span>
<span class="k">def</span> <span class="nf">test_feature_one</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="c"># Test feature one.</span>
<span class="o">...</span> <span class="n">testing</span> <span class="n">code</span> <span class="o">...</span>
<span class="k">def</span> <span class="nf">test_feature_two</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="c"># Test feature two.</span>
<span class="o">...</span> <span class="n">testing</span> <span class="n">code</span> <span class="o">...</span>
<span class="o">...</span> <span class="n">more</span> <span class="n">test</span> <span class="n">methods</span> <span class="o">...</span>
<span class="k">class</span> <span class="nc">MyTestCase2</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>
<span class="o">...</span> <span class="n">same</span> <span class="n">structure</span> <span class="k">as</span> <span class="n">MyTestCase1</span> <span class="o">...</span>
<span class="o">...</span> <span class="n">more</span> <span class="n">test</span> <span class="n">classes</span> <span class="o">...</span>
<span class="k">def</span> <span class="nf">test_main</span><span class="p">():</span>
<span class="n">support</span><span class="o">.</span><span class="n">run_unittest</span><span class="p">(</span><span class="n">MyTestCase1</span><span class="p">,</span>
<span class="n">MyTestCase2</span><span class="p">,</span>
<span class="o">...</span> <span class="nb">list</span> <span class="n">other</span> <span class="n">tests</span> <span class="o">...</span>
<span class="p">)</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">test_main</span><span class="p">()</span>
</pre></div>
</div>
<p>This boilerplate code allows the testing suite to be run by <tt class="xref py py-mod docutils literal"><span class="pre">test.regrtest</span></tt>
as well as on its own as a script.</p>
<p>The goal for regression testing is to try to break code. This leads to a few
guidelines to be followed:</p>
<ul>
<li><p class="first">The testing suite should exercise all classes, functions, and constants. This
includes not just the external API that is to be presented to the outside
world but also “private” code.</p>
</li>
<li><p class="first">Whitebox testing (examining the code being tested when the tests are being
written) is preferred. Blackbox testing (testing only the published user
interface) is not complete enough to make sure all boundary and edge cases
are tested.</p>
</li>
<li><p class="first">Make sure all possible values are tested including invalid ones. This makes
sure that not only all valid values are acceptable but also that improper
values are handled correctly.</p>
</li>
<li><p class="first">Exhaust as many code paths as possible. Test where branching occurs and thus
tailor input to make sure as many different paths through the code are taken.</p>
</li>
<li><p class="first">Add an explicit test for any bugs discovered for the tested code. This will
make sure that the error does not crop up again if the code is changed in the
future.</p>
</li>
<li><p class="first">Make sure to clean up after your tests (such as close and remove all temporary
files).</p>
</li>
<li><p class="first">If a test is dependent on a specific condition of the operating system then
verify the condition already exists before attempting the test.</p>
</li>
<li><p class="first">Import as few modules as possible and do it as soon as possible. This
minimizes external dependencies of tests and also minimizes possible anomalous
behavior from side-effects of importing a module.</p>
</li>
<li><p class="first">Try to maximize code reuse. On occasion, tests will vary by something as small
as what type of input is used. Minimize code duplication by subclassing a
basic test class with a class that specifies the input:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="k">class</span> <span class="nc">TestFuncAcceptsSequences</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>
<span class="n">func</span> <span class="o">=</span> <span class="n">mySuperWhammyFunction</span>
<span class="k">def</span> <span class="nf">test_func</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">func</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">arg</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">AcceptLists</span><span class="p">(</span><span class="n">TestFuncAcceptsSequences</span><span class="p">):</span>
<span class="n">arg</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">3</span><span class="p">]</span>
<span class="k">class</span> <span class="nc">AcceptStrings</span><span class="p">(</span><span class="n">TestFuncAcceptsSequences</span><span class="p">):</span>
<span class="n">arg</span> <span class="o">=</span> <span class="s">'abc'</span>
<span class="k">class</span> <span class="nc">AcceptTuples</span><span class="p">(</span><span class="n">TestFuncAcceptsSequences</span><span class="p">):</span>
<span class="n">arg</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">3</span><span class="p">)</span>
</pre></div>
</div>
</li>
</ul>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt>Test Driven Development</dt>
<dd>A book by Kent Beck on writing tests before code.</dd>
</dl>
</div>
</div>
<div class="section" id="running-tests-using-the-command-line-interface">
<span id="regrtest"></span><h2>25.5.2. Running tests using the command-line interface<a class="headerlink" href="#running-tests-using-the-command-line-interface" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference internal" href="#module-test" title="test: Regression tests package containing the testing suite for Python."><tt class="xref py py-mod docutils literal"><span class="pre">test</span></tt></a> package can be run as a script to drive Python’s regression
test suite, thanks to the <a class="reference internal" href="../using/cmdline.html#cmdoption-m"><em class="xref std std-option">-m</em></a> option: <strong class="program">python -m test</strong>. Under
the hood, it uses <tt class="xref py py-mod docutils literal"><span class="pre">test.regrtest</span></tt>; the call <strong class="program">python -m
test.regrtest</strong> used in previous Python versions still works).
Running the script by itself automatically starts running all regression
tests in the <a class="reference internal" href="#module-test" title="test: Regression tests package containing the testing suite for Python."><tt class="xref py py-mod docutils literal"><span class="pre">test</span></tt></a> package. It does this by finding all modules in the
package whose name starts with <tt class="docutils literal"><span class="pre">test_</span></tt>, importing them, and executing the
function <tt class="xref py py-func docutils literal"><span class="pre">test_main()</span></tt> if present. The names of tests to execute may also
be passed to the script. Specifying a single regression test (<strong class="program">python
-m test test_spam</strong>) will minimize output and only print
whether the test passed or failed and thus minimize output.</p>
<p>Running <a class="reference internal" href="#module-test" title="test: Regression tests package containing the testing suite for Python."><tt class="xref py py-mod docutils literal"><span class="pre">test</span></tt></a> directly allows what resources are available for
tests to use to be set. You do this by using the <tt class="docutils literal"><span class="pre">-u</span></tt> command-line
option. Run <strong class="program">python -m test -uall</strong> to turn on all
resources; specifying <tt class="docutils literal"><span class="pre">all</span></tt> as an option for <tt class="docutils literal"><span class="pre">-u</span></tt> enables all
possible resources. If all but one resource is desired (a more common case), a
comma-separated list of resources that are not desired may be listed after
<tt class="docutils literal"><span class="pre">all</span></tt>. The command <strong class="program">python -m test -uall,-audio,-largefile</strong>
will run <a class="reference internal" href="#module-test" title="test: Regression tests package containing the testing suite for Python."><tt class="xref py py-mod docutils literal"><span class="pre">test</span></tt></a> with all resources except the <tt class="docutils literal"><span class="pre">audio</span></tt> and
<tt class="docutils literal"><span class="pre">largefile</span></tt> resources. For a list of all resources and more command-line
options, run <strong class="program">python -m test -h</strong>.</p>
<p>Some other ways to execute the regression tests depend on what platform the
tests are being executed on. On Unix, you can run <strong class="program">make test</strong> at the
top-level directory where Python was built. On Windows,
executing <strong class="program">rt.bat</strong> from your <tt class="file docutils literal"><span class="pre">PCBuild</span></tt> directory will run all
regression tests.</p>
</div>
</div>
<div class="section" id="module-test.support">
<span id="test-support-utilities-for-the-python-test-suite"></span><h1>25.6. <a class="reference internal" href="#module-test.support" title="test.support: Support for Python's regression test suite."><tt class="xref py py-mod docutils literal"><span class="pre">test.support</span></tt></a> — Utilities for the Python test suite<a class="headerlink" href="#module-test.support" title="Permalink to this headline">¶</a></h1>
<p>The <a class="reference internal" href="#module-test.support" title="test.support: Support for Python's regression test suite."><tt class="xref py py-mod docutils literal"><span class="pre">test.support</span></tt></a> module provides support for Python’s regression
test suite.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last"><a class="reference internal" href="#module-test.support" title="test.support: Support for Python's regression test suite."><tt class="xref py py-mod docutils literal"><span class="pre">test.support</span></tt></a> is not a public module. It is documented here to help
Python developers write tests. The API of this module is subject to change
without backwards compatibility concerns between releases.</p>
</div>
<p>This module defines the following exceptions:</p>
<dl class="exception">
<dt id="test.support.TestFailed">
<em class="property">exception </em><tt class="descclassname">test.support.</tt><tt class="descname">TestFailed</tt><a class="headerlink" href="#test.support.TestFailed" title="Permalink to this definition">¶</a></dt>
<dd><p>Exception to be raised when a test fails. This is deprecated in favor of
<a class="reference internal" href="unittest.html#module-unittest" title="unittest: Unit testing framework for Python."><tt class="xref py py-mod docutils literal"><span class="pre">unittest</span></tt></a>-based tests and <a class="reference internal" href="unittest.html#unittest.TestCase" title="unittest.TestCase"><tt class="xref py py-class docutils literal"><span class="pre">unittest.TestCase</span></tt></a>‘s assertion
methods.</p>
</dd></dl>
<dl class="exception">
<dt id="test.support.ResourceDenied">
<em class="property">exception </em><tt class="descclassname">test.support.</tt><tt class="descname">ResourceDenied</tt><a class="headerlink" href="#test.support.ResourceDenied" title="Permalink to this definition">¶</a></dt>
<dd><p>Subclass of <tt class="xref py py-exc docutils literal"><span class="pre">unittest.SkipTest</span></tt>. Raised when a resource (such as a
network connection) is not available. Raised by the <a class="reference internal" href="#test.support.requires" title="test.support.requires"><tt class="xref py py-func docutils literal"><span class="pre">requires()</span></tt></a>
function.</p>
</dd></dl>
<p>The <a class="reference internal" href="#module-test.support" title="test.support: Support for Python's regression test suite."><tt class="xref py py-mod docutils literal"><span class="pre">test.support</span></tt></a> module defines the following constants:</p>
<dl class="data">
<dt id="test.support.verbose">
<tt class="descclassname">test.support.</tt><tt class="descname">verbose</tt><a class="headerlink" href="#test.support.verbose" title="Permalink to this definition">¶</a></dt>
<dd><p><a class="reference internal" href="constants.html#True" title="True"><tt class="xref py py-const xref docutils literal"><span class="pre">True</span></tt></a> when verbose output is enabled. Should be checked when more
detailed information is desired about a running test. <em>verbose</em> is set by
<tt class="xref py py-mod docutils literal"><span class="pre">test.regrtest</span></tt>.</p>
</dd></dl>
<dl class="data">
<dt id="test.support.is_jython">
<tt class="descclassname">test.support.</tt><tt class="descname">is_jython</tt><a class="headerlink" href="#test.support.is_jython" title="Permalink to this definition">¶</a></dt>
<dd><p><a class="reference internal" href="constants.html#True" title="True"><tt class="xref py py-const xref docutils literal"><span class="pre">True</span></tt></a> if the running interpreter is Jython.</p>
</dd></dl>
<dl class="data">
<dt id="test.support.TESTFN">
<tt class="descclassname">test.support.</tt><tt class="descname">TESTFN</tt><a class="headerlink" href="#test.support.TESTFN" title="Permalink to this definition">¶</a></dt>
<dd><p>Set to a name that is safe to use as the name of a temporary file. Any
temporary file that is created should be closed and unlinked (removed).</p>
</dd></dl>
<p>The <a class="reference internal" href="#module-test.support" title="test.support: Support for Python's regression test suite."><tt class="xref py py-mod docutils literal"><span class="pre">test.support</span></tt></a> module defines the following functions:</p>
<dl class="function">
<dt id="test.support.forget">
<tt class="descclassname">test.support.</tt><tt class="descname">forget</tt><big>(</big><em>module_name</em><big>)</big><a class="headerlink" href="#test.support.forget" title="Permalink to this definition">¶</a></dt>
<dd><p>Remove the module named <em>module_name</em> from <tt class="docutils literal"><span class="pre">sys.modules</span></tt> and delete any
byte-compiled files of the module.</p>
</dd></dl>
<dl class="function">
<dt id="test.support.is_resource_enabled">
<tt class="descclassname">test.support.</tt><tt class="descname">is_resource_enabled</tt><big>(</big><em>resource</em><big>)</big><a class="headerlink" href="#test.support.is_resource_enabled" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <a class="reference internal" href="constants.html#True" title="True"><tt class="xref py py-const xref docutils literal"><span class="pre">True</span></tt></a> if <em>resource</em> is enabled and available. The list of
available resources is only set when <tt class="xref py py-mod docutils literal"><span class="pre">test.regrtest</span></tt> is executing the
tests.</p>
</dd></dl>
<dl class="function">
<dt id="test.support.requires">
<tt class="descclassname">test.support.</tt><tt class="descname">requires</tt><big>(</big><em>resource</em>, <em>msg=None</em><big>)</big><a class="headerlink" href="#test.support.requires" title="Permalink to this definition">¶</a></dt>
<dd><p>Raise <a class="reference internal" href="#test.support.ResourceDenied" title="test.support.ResourceDenied"><tt class="xref py py-exc docutils literal"><span class="pre">ResourceDenied</span></tt></a> if <em>resource</em> is not available. <em>msg</em> is the
argument to <a class="reference internal" href="#test.support.ResourceDenied" title="test.support.ResourceDenied"><tt class="xref py py-exc docutils literal"><span class="pre">ResourceDenied</span></tt></a> if it is raised. Always returns
<a class="reference internal" href="constants.html#True" title="True"><tt class="xref py py-const xref docutils literal"><span class="pre">True</span></tt></a> if called by a function whose <tt class="docutils literal"><span class="pre">__name__</span></tt> is <tt class="docutils literal"><span class="pre">'__main__'</span></tt>.
Used when tests are executed by <tt class="xref py py-mod docutils literal"><span class="pre">test.regrtest</span></tt>.</p>
</dd></dl>
<dl class="function">
<dt id="test.support.findfile">
<tt class="descclassname">test.support.</tt><tt class="descname">findfile</tt><big>(</big><em>filename</em><big>)</big><a class="headerlink" href="#test.support.findfile" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the path to the file named <em>filename</em>. If no match is found
<em>filename</em> is returned. This does not equal a failure since it could be the
path to the file.</p>
</dd></dl>
<dl class="function">
<dt id="test.support.run_unittest">
<tt class="descclassname">test.support.</tt><tt class="descname">run_unittest</tt><big>(</big><em>*classes</em><big>)</big><a class="headerlink" href="#test.support.run_unittest" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute <a class="reference internal" href="unittest.html#unittest.TestCase" title="unittest.TestCase"><tt class="xref py py-class docutils literal"><span class="pre">unittest.TestCase</span></tt></a> subclasses passed to the function. The
function scans the classes for methods starting with the prefix <tt class="docutils literal"><span class="pre">test_</span></tt>
and executes the tests individually.</p>
<p>It is also legal to pass strings as parameters; these should be keys in
<tt class="docutils literal"><span class="pre">sys.modules</span></tt>. Each associated module will be scanned by
<tt class="docutils literal"><span class="pre">unittest.TestLoader.loadTestsFromModule()</span></tt>. This is usually seen in the
following <tt class="xref py py-func docutils literal"><span class="pre">test_main()</span></tt> function:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="k">def</span> <span class="nf">test_main</span><span class="p">():</span>
<span class="n">support</span><span class="o">.</span><span class="n">run_unittest</span><span class="p">(</span><span class="n">__name__</span><span class="p">)</span>
</pre></div>
</div>
<p>This will run all tests defined in the named module.</p>
</dd></dl>
<dl class="function">
<dt id="test.support.check_warnings">
<tt class="descclassname">test.support.</tt><tt class="descname">check_warnings</tt><big>(</big><em>*filters</em>, <em>quiet=True</em><big>)</big><a class="headerlink" href="#test.support.check_warnings" title="Permalink to this definition">¶</a></dt>
<dd><p>A convenience wrapper for <a class="reference internal" href="warnings.html#warnings.catch_warnings" title="warnings.catch_warnings"><tt class="xref py py-func docutils literal"><span class="pre">warnings.catch_warnings()</span></tt></a> that makes it
easier to test that a warning was correctly raised. It is approximately
equivalent to calling <tt class="docutils literal"><span class="pre">warnings.catch_warnings(record=True)</span></tt> with
<a class="reference internal" href="warnings.html#warnings.simplefilter" title="warnings.simplefilter"><tt class="xref py py-meth docutils literal"><span class="pre">warnings.simplefilter()</span></tt></a> set to <tt class="docutils literal"><span class="pre">always</span></tt> and with the option to
automatically validate the results that are recorded.</p>
<p><tt class="docutils literal"><span class="pre">check_warnings</span></tt> accepts 2-tuples of the form <tt class="docutils literal"><span class="pre">("message</span> <span class="pre">regexp",</span>
<span class="pre">WarningCategory)</span></tt> as positional arguments. If one or more <em>filters</em> are
provided, or if the optional keyword argument <em>quiet</em> is <a class="reference internal" href="constants.html#False" title="False"><tt class="xref py py-const xref docutils literal"><span class="pre">False</span></tt></a>,
it checks to make sure the warnings are as expected: each specified filter
must match at least one of the warnings raised by the enclosed code or the
test fails, and if any warnings are raised that do not match any of the
specified filters the test fails. To disable the first of these checks,
set <em>quiet</em> to <a class="reference internal" href="constants.html#True" title="True"><tt class="xref py py-const xref docutils literal"><span class="pre">True</span></tt></a>.</p>
<p>If no arguments are specified, it defaults to:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">check_warnings</span><span class="p">((</span><span class="s">""</span><span class="p">,</span> <span class="ne">Warning</span><span class="p">),</span> <span class="n">quiet</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
</pre></div>
</div>
<p>In this case all warnings are caught and no errors are raised.</p>
<p>On entry to the context manager, a <tt class="xref py py-class docutils literal"><span class="pre">WarningRecorder</span></tt> instance is
returned. The underlying warnings list from
<a class="reference internal" href="warnings.html#warnings.catch_warnings" title="warnings.catch_warnings"><tt class="xref py py-func docutils literal"><span class="pre">catch_warnings()</span></tt></a> is available via the recorder object’s
<a class="reference internal" href="warnings.html#module-warnings" title="warnings: Issue warning messages and control their disposition."><tt class="xref py py-attr docutils literal"><span class="pre">warnings</span></tt></a> attribute. As a convenience, the attributes of the object
representing the most recent warning can also be accessed directly through
the recorder object (see example below). If no warning has been raised,
then any of the attributes that would otherwise be expected on an object
representing a warning will return <a class="reference internal" href="constants.html#None" title="None"><tt class="xref py py-const xref docutils literal"><span class="pre">None</span></tt></a>.</p>
<p>The recorder object also has a <tt class="xref py py-meth docutils literal"><span class="pre">reset()</span></tt> method, which clears the
warnings list.</p>
<p>The context manager is designed to be used like this:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="k">with</span> <span class="n">check_warnings</span><span class="p">((</span><span class="s">"assertion is always true"</span><span class="p">,</span> <span class="ne">SyntaxWarning</span><span class="p">),</span>
<span class="p">(</span><span class="s">""</span><span class="p">,</span> <span class="ne">UserWarning</span><span class="p">)):</span>
<span class="n">exec</span><span class="p">(</span><span class="s">'assert(False, "Hey!")'</span><span class="p">)</span>
<span class="n">warnings</span><span class="o">.</span><span class="n">warn</span><span class="p">(</span><span class="ne">UserWarning</span><span class="p">(</span><span class="s">"Hide me!"</span><span class="p">))</span>
</pre></div>
</div>
<p>In this case if either warning was not raised, or some other warning was
raised, <a class="reference internal" href="#test.support.check_warnings" title="test.support.check_warnings"><tt class="xref py py-func docutils literal"><span class="pre">check_warnings()</span></tt></a> would raise an error.</p>
<p>When a test needs to look more deeply into the warnings, rather than
just checking whether or not they occurred, code like this can be used:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="k">with</span> <span class="n">check_warnings</span><span class="p">(</span><span class="n">quiet</span><span class="o">=</span><span class="k">True</span><span class="p">)</span> <span class="k">as</span> <span class="n">w</span><span class="p">:</span>
<span class="n">warnings</span><span class="o">.</span><span class="n">warn</span><span class="p">(</span><span class="s">"foo"</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">str</span><span class="p">(</span><span class="n">w</span><span class="o">.</span><span class="n">args</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span> <span class="o">==</span> <span class="s">"foo"</span>
<span class="n">warnings</span><span class="o">.</span><span class="n">warn</span><span class="p">(</span><span class="s">"bar"</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">str</span><span class="p">(</span><span class="n">w</span><span class="o">.</span><span class="n">args</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span> <span class="o">==</span> <span class="s">"bar"</span>
<span class="k">assert</span> <span class="nb">str</span><span class="p">(</span><span class="n">w</span><span class="o">.</span><span class="n">warnings</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">args</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span> <span class="o">==</span> <span class="s">"foo"</span>
<span class="k">assert</span> <span class="nb">str</span><span class="p">(</span><span class="n">w</span><span class="o">.</span><span class="n">warnings</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">args</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span> <span class="o">==</span> <span class="s">"bar"</span>
<span class="n">w</span><span class="o">.</span><span class="n">reset</span><span class="p">()</span>
<span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">w</span><span class="o">.</span><span class="n">warnings</span><span class="p">)</span> <span class="o">==</span> <span class="mi">0</span>
</pre></div>
</div>
<p>Here all warnings will be caught, and the test code tests the captured
warnings directly.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 3.2: </span>New optional arguments <em>filters</em> and <em>quiet</em>.</p>
</dd></dl>
<dl class="function">
<dt id="test.support.captured_stdout">
<tt class="descclassname">test.support.</tt><tt class="descname">captured_stdout</tt><big>(</big><big>)</big><a class="headerlink" href="#test.support.captured_stdout" title="Permalink to this definition">¶</a></dt>
<dd><p>This is a context manager that runs the <a class="reference internal" href="../reference/compound_stmts.html#with"><tt class="xref std std-keyword docutils literal"><span class="pre">with</span></tt></a> statement body using
a <tt class="xref py py-class docutils literal"><span class="pre">StringIO.StringIO</span></tt> object as sys.stdout. That object can be
retrieved using the <tt class="docutils literal"><span class="pre">as</span></tt> clause of the <a class="reference internal" href="../reference/compound_stmts.html#with"><tt class="xref std std-keyword docutils literal"><span class="pre">with</span></tt></a> statement.</p>
<p>Example use:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="k">with</span> <span class="n">captured_stdout</span><span class="p">()</span> <span class="k">as</span> <span class="n">s</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="s">"hello"</span><span class="p">)</span>
<span class="k">assert</span> <span class="n">s</span><span class="o">.</span><span class="n">getvalue</span><span class="p">()</span> <span class="o">==</span> <span class="s">"hello"</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="test.support.import_module">
<tt class="descclassname">test.support.</tt><tt class="descname">import_module</tt><big>(</big><em>name</em>, <em>deprecated=False</em><big>)</big><a class="headerlink" href="#test.support.import_module" title="Permalink to this definition">¶</a></dt>
<dd><p>This function imports and returns the named module. Unlike a normal
import, this function raises <tt class="xref py py-exc docutils literal"><span class="pre">unittest.SkipTest</span></tt> if the module
cannot be imported.</p>
<p>Module and package deprecation messages are suppressed during this import
if <em>deprecated</em> is <a class="reference internal" href="constants.html#True" title="True"><tt class="xref py py-const xref docutils literal"><span class="pre">True</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.1.</span></p>
</dd></dl>
<dl class="function">
<dt id="test.support.import_fresh_module">
<tt class="descclassname">test.support.</tt><tt class="descname">import_fresh_module</tt><big>(</big><em>name</em>, <em>fresh=()</em>, <em>blocked=()</em>, <em>deprecated=False</em><big>)</big><a class="headerlink" href="#test.support.import_fresh_module" title="Permalink to this definition">¶</a></dt>
<dd><p>This function imports and returns a fresh copy of the named Python module
by removing the named module from <tt class="docutils literal"><span class="pre">sys.modules</span></tt> before doing the import.
Note that unlike <tt class="xref py py-func docutils literal"><span class="pre">reload()</span></tt>, the original module is not affected by
this operation.</p>
<p><em>fresh</em> is an iterable of additional module names that are also removed
from the <tt class="docutils literal"><span class="pre">sys.modules</span></tt> cache before doing the import.</p>
<p><em>blocked</em> is an iterable of module names that are replaced with <tt class="xref py py-const docutils literal"><span class="pre">0</span></tt>
in the module cache during the import to ensure that attempts to import
them raise <a class="reference internal" href="exceptions.html#ImportError" title="ImportError"><tt class="xref py py-exc docutils literal"><span class="pre">ImportError</span></tt></a>.</p>
<p>The named module and any modules named in the <em>fresh</em> and <em>blocked</em>
parameters are saved before starting the import and then reinserted into
<tt class="docutils literal"><span class="pre">sys.modules</span></tt> when the fresh import is complete.</p>
<p>Module and package deprecation messages are suppressed during this import
if <em>deprecated</em> is <a class="reference internal" href="constants.html#True" title="True"><tt class="xref py py-const xref docutils literal"><span class="pre">True</span></tt></a>.</p>
<p>This function will raise <tt class="xref py py-exc docutils literal"><span class="pre">unittest.SkipTest</span></tt> is the named module
cannot be imported.</p>
<p>Example use:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="c"># Get copies of the warnings module for testing without</span>
<span class="c"># affecting the version being used by the rest of the test suite</span>
<span class="c"># One copy uses the C implementation, the other is forced to use</span>
<span class="c"># the pure Python fallback implementation</span>
<span class="n">py_warnings</span> <span class="o">=</span> <span class="n">import_fresh_module</span><span class="p">(</span><span class="s">'warnings'</span><span class="p">,</span> <span class="n">blocked</span><span class="o">=</span><span class="p">[</span><span class="s">'_warnings'</span><span class="p">])</span>
<span class="n">c_warnings</span> <span class="o">=</span> <span class="n">import_fresh_module</span><span class="p">(</span><span class="s">'warnings'</span><span class="p">,</span> <span class="n">fresh</span><span class="o">=</span><span class="p">[</span><span class="s">'_warnings'</span><span class="p">])</span>
</pre></div>
</div>
<p class="versionadded">
<span class="versionmodified">New in version 3.1.</span></p>
</dd></dl>
<p>The <a class="reference internal" href="#module-test.support" title="test.support: Support for Python's regression test suite."><tt class="xref py py-mod docutils literal"><span class="pre">test.support</span></tt></a> module defines the following classes:</p>
<dl class="class">
<dt id="test.support.TransientResource">
<em class="property">class </em><tt class="descclassname">test.support.</tt><tt class="descname">TransientResource</tt><big>(</big><em>exc</em>, <em>**kwargs</em><big>)</big><a class="headerlink" href="#test.support.TransientResource" title="Permalink to this definition">¶</a></dt>
<dd><p>Instances are a context manager that raises <a class="reference internal" href="#test.support.ResourceDenied" title="test.support.ResourceDenied"><tt class="xref py py-exc docutils literal"><span class="pre">ResourceDenied</span></tt></a> if the
specified exception type is raised. Any keyword arguments are treated as
attribute/value pairs to be compared against any exception raised within the
<a class="reference internal" href="../reference/compound_stmts.html#with"><tt class="xref std std-keyword docutils literal"><span class="pre">with</span></tt></a> statement. Only if all pairs match properly against
attributes on the exception is <a class="reference internal" href="#test.support.ResourceDenied" title="test.support.ResourceDenied"><tt class="xref py py-exc docutils literal"><span class="pre">ResourceDenied</span></tt></a> raised.</p>
</dd></dl>
<dl class="class">
<dt id="test.support.EnvironmentVarGuard">
<em class="property">class </em><tt class="descclassname">test.support.</tt><tt class="descname">EnvironmentVarGuard</tt><a class="headerlink" href="#test.support.EnvironmentVarGuard" title="Permalink to this definition">¶</a></dt>
<dd><p>Class used to temporarily set or unset environment variables. Instances can
be used as a context manager and have a complete dictionary interface for
querying/modifying the underlying <tt class="docutils literal"><span class="pre">os.environ</span></tt>. After exit from the
context manager all changes to environment variables done through this
instance will be rolled back.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 3.1: </span>Added dictionary interface.</p>
</dd></dl>
<dl class="method">
<dt id="test.support.EnvironmentVarGuard.set">
<tt class="descclassname">EnvironmentVarGuard.</tt><tt class="descname">set</tt><big>(</big><em>envvar</em>, <em>value</em><big>)</big><a class="headerlink" href="#test.support.EnvironmentVarGuard.set" title="Permalink to this definition">¶</a></dt>
<dd><p>Temporarily set the environment variable <tt class="docutils literal"><span class="pre">envvar</span></tt> to the value of
<tt class="docutils literal"><span class="pre">value</span></tt>.</p>
</dd></dl>
<dl class="method">
<dt id="test.support.EnvironmentVarGuard.unset">
<tt class="descclassname">EnvironmentVarGuard.</tt><tt class="descname">unset</tt><big>(</big><em>envvar</em><big>)</big><a class="headerlink" href="#test.support.EnvironmentVarGuard.unset" title="Permalink to this definition">¶</a></dt>
<dd><p>Temporarily unset the environment variable <tt class="docutils literal"><span class="pre">envvar</span></tt>.</p>
</dd></dl>
<dl class="class">
<dt id="test.support.WarningsRecorder">
<em class="property">class </em><tt class="descclassname">test.support.</tt><tt class="descname">WarningsRecorder</tt><a class="headerlink" href="#test.support.WarningsRecorder" title="Permalink to this definition">¶</a></dt>
<dd><p>Class used to record warnings for unit tests. See documentation of
<a class="reference internal" href="#test.support.check_warnings" title="test.support.check_warnings"><tt class="xref py py-func docutils literal"><span class="pre">check_warnings()</span></tt></a> above for more details.</p>
</dd></dl>
</div>
</div>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">25.5. <tt class="docutils literal"><span class="pre">test</span></tt> — Regression tests package for Python</a><ul>
<li><a class="reference internal" href="#writing-unit-tests-for-the-test-package">25.5.1. Writing Unit Tests for the <tt class="docutils literal"><span class="pre">test</span></tt> package</a></li>
<li><a class="reference internal" href="#running-tests-using-the-command-line-interface">25.5.2. Running tests using the command-line interface</a></li>
</ul>
</li>
<li><a class="reference internal" href="#module-test.support">25.6. <tt class="docutils literal"><span class="pre">test.support</span></tt> — Utilities for the Python test suite</a></li>
</ul>
<h4>Previous topic</h4>
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