~crunch.io/ubuntu/precise/codespeak-lib/unstable

<li><a class="reference internal" href="#capturing-of-input-output-streams-during-tests" id="id1">Capturing of input/output streams during tests</a></li>

<li><a class="reference internal" href="#sys-level-capturing" id="id2">sys-level capturing</a></li>

<li><a class="reference internal" href="#fd-level-capturing-and-subprocesses" id="id3">FD-level capturing and subprocesses</a></li>

<li><a class="reference internal" href="#example-usage-of-the-capturing-function-arguments" id="id4">Example Usage of the capturing Function arguments</a></li>

<li><a class="reference internal" href="#the-capsys-test-function-argument" id="id5">the 'capsys' test function argument</a></li>

<li><a class="reference internal" href="#the-capfd-test-function-argument" id="id6">the 'capfd' test function argument</a></li>

<li><a class="reference internal" href="#command-line-options" id="id7">command line options</a></li>

</ul>

</div>

<p>This plugin captures stdout/stderr output for each test separately.

In case of test failures this captured output is shown grouped

togtther with the test.</p>

<p>The plugin also provides test function arguments that help to

assert stdout/stderr output from within your tests, see the

<a class="reference internal" href="#funcarg-example">funcarg example</a>.</p>

<h2><a class="toc-backref" href="#id1">Capturing of input/output streams during tests</a></h2>

<p>By default <tt class="docutils literal">sys.stdout</tt> and <tt class="docutils literal">sys.stderr</tt> are substituted with

temporary streams during the execution of tests and setup/teardown code.

During the whole testing process it will re-use the same temporary

streams allowing to play well with the logging module which easily

takes ownership on these streams.</p>

<p>Also, 'sys.stdin' is substituted with a file-like "null" object that

does not return any values. This is to immediately error out

on tests that wait on reading something from stdin.</p>

<p>You can influence output capturing mechanisms from the command line:</p>

py.test -s # disable all capturing

py.test --capture=sys # replace sys.stdout/stderr with in-mem files

py.test --capture=fd # point filedescriptors 1 and 2 to temp file

</pre>

<p>If you set capturing values in a conftest file like this:</p>

# conftest.py

option_capture = 'fd'

</pre>

<p>then all tests in that directory will execute with "fd" style capturing.</p>

</div>

<h2><a class="toc-backref" href="#id2">sys-level capturing</a></h2>

<p>Capturing on 'sys' level means that <tt class="docutils literal">sys.stdout</tt> and <tt class="docutils literal">sys.stderr</tt>

will be replaced with in-memory files (<tt class="docutils literal">py.io.TextIO</tt> to be precise)

that capture writes and decode non-unicode strings to a unicode object

(using a default, usually, UTF-8, encoding).</p>

</div>

<h2><a class="toc-backref" href="#id3">FD-level capturing and subprocesses</a></h2>

<p>The <tt class="docutils literal">fd</tt> based method means that writes going to system level files

based on the standard file descriptors will be captured, for example

writes such as <tt class="docutils literal">os.write(1, 'hello')</tt> will be captured properly.

Capturing on fd-level will include output generated from

any subprocesses created during a test.</p>

</div>

<span id="funcarg-example"></span><h2><a class="toc-backref" href="#id4">Example Usage of the capturing Function arguments</a></h2>

<p>You can use the <a class="reference internal" href="#capsys-funcarg">capsys funcarg</a> and <a class="reference internal" href="#capfd-funcarg">capfd funcarg</a> to

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capture writes to stdout and stderr streams. Using the

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funcargs frees your test from having to care about setting/resetting

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the old streams and also interacts well with py.test's own

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per-test capturing. Here is an example test function:</p>

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<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #008000; font-weight: bold">def</span> <span style="color: #0000FF">test_myoutput</span>(capsys):

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<span style="color: #008000; font-weight: bold">print</span> (<span style="color: #BA2121">"hello"</span>)

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sys<span style="color: #666666">.</span>stderr<span style="color: #666666">.</span>write(<span style="color: #BA2121">"world</span><span style="color: #BB6622; font-weight: bold">\n</span><span style="color: #BA2121">"</span>)

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out, err <span style="color: #666666">=</span> capsys<span style="color: #666666">.</span>readouterr()

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<span style="color: #008000; font-weight: bold">assert</span> out <span style="color: #666666">==</span> <span style="color: #BA2121">"hello</span><span style="color: #BB6622; font-weight: bold">\n</span><span style="color: #BA2121">"</span>

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<span style="color: #008000; font-weight: bold">assert</span> err <span style="color: #666666">==</span> <span style="color: #BA2121">"world</span><span style="color: #BB6622; font-weight: bold">\n</span><span style="color: #BA2121">"</span>

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<span style="color: #008000; font-weight: bold">print</span> <span style="color: #BA2121">"next"</span>

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out, err <span style="color: #666666">=</span> capsys<span style="color: #666666">.</span>readouterr()

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<span style="color: #008000; font-weight: bold">assert</span> out <span style="color: #666666">==</span> <span style="color: #BA2121">"next</span><span style="color: #BB6622; font-weight: bold">\n</span><span style="color: #BA2121">"</span>

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</pre></div>

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<p>The <tt class="docutils literal">readouterr()</tt> call snapshots the output so far -

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and capturing will be continued. After the test

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function finishes the original streams will

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be restored. If you want to capture on

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the filedescriptor level you can use the <tt class="docutils literal">capfd</tt> function

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argument which offers the same interface.</p>

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</div>

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<span id="capsys-funcarg"></span><h2><a class="toc-backref" href="#id5">the 'capsys' test function argument</a></h2>

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<p>captures writes to sys.stdout/sys.stderr and makes

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them available successively via a <tt class="docutils literal">capsys.readouterr()</tt> method

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which returns a <tt class="docutils literal">(out, err)</tt> tuple of captured snapshot strings.</p>

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</div>

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<span id="capfd-funcarg"></span><h2><a class="toc-backref" href="#id6">the 'capfd' test function argument</a></h2>

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<p>captures writes to file descriptors 1 and 2 and makes

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snapshotted <tt class="docutils literal">(out, err)</tt> string tuples available

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via the <tt class="docutils literal">capsys.readouterr()</tt> method. If the underlying

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platform does not have <tt class="docutils literal">os.dup</tt> (e.g. Jython) tests using

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this funcarg will automatically skip.</p>

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</div>

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<h2><a class="toc-backref" href="#id7">command line options</a></h2>

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<dt><tt class="docutils literal"><span class="pre">--capture=method</span></tt></dt>

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<dd>per-test capturing method: one of fd (default)|sys|no.</dd>

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<dd>shortcut for --capture=no.</dd>

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</dl>

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</div>

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</div>

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<h1>Start improving this plugin in 30 seconds</h1>

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<li>Download <a class="reference external" href="http://bitbucket.org/hpk42/py-trunk/raw/1.2.0/py/_plugin/pytest_capture.py">pytest_capture.py</a> plugin source code</li>

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<li>put it somewhere as <tt class="docutils literal">pytest_capture.py</tt> into your import path</li>

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<li>a subsequent <tt class="docutils literal">py.test</tt> run will use your local version</li>

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</ol>

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<p>Checkout <a class="reference external" href="../customize.html">customize</a>, other <a class="reference external" href="index.html">plugins</a> or <a class="reference external" href="../../contact.html">get in contact</a>.</p>

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