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  <div class="section" id="asserting-warnings">
<h1>Asserting Warnings<a class="headerlink" href="#asserting-warnings" title="Permalink to this headline"></a></h1>
<div class="section" id="asserting-warnings-with-the-warns-function">
<span id="warns"></span><h2>Asserting warnings with the warns function<a class="headerlink" href="#asserting-warnings-with-the-warns-function" title="Permalink to this headline"></a></h2>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.8.</span></p>
</div>
<p>You can check that code raises a particular warning using <code class="docutils literal"><span class="pre">pytest.warns</span></code>,
which works in a similar manner to <a class="reference internal" href="assert.html#assertraises"><span>raises</span></a>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">warnings</span>
<span class="kn">import</span> <span class="nn">pytest</span>

<span class="k">def</span> <span class="nf">test_warning</span><span class="p">():</span>
    <span class="k">with</span> <span class="n">pytest</span><span class="o">.</span><span class="n">warns</span><span class="p">(</span><span class="ne">UserWarning</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="s2">&quot;my warning&quot;</span><span class="p">,</span> <span class="ne">UserWarning</span><span class="p">)</span>
</pre></div>
</div>
<p>The test will fail if the warning in question is not raised.</p>
<p>You can also call <code class="docutils literal"><span class="pre">pytest.warns</span></code> on a function or code string:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">pytest</span><span class="o">.</span><span class="n">warns</span><span class="p">(</span><span class="n">expected_warning</span><span class="p">,</span> <span class="n">func</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span>
<span class="n">pytest</span><span class="o">.</span><span class="n">warns</span><span class="p">(</span><span class="n">expected_warning</span><span class="p">,</span> <span class="s2">&quot;func(*args, **kwargs)&quot;</span><span class="p">)</span>
</pre></div>
</div>
<p>The function also returns a list of all raised warnings (as
<code class="docutils literal"><span class="pre">warnings.WarningMessage</span></code> objects), which you can query for
additional information:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">with</span> <span class="n">pytest</span><span class="o">.</span><span class="n">warns</span><span class="p">(</span><span class="ne">RuntimeWarning</span><span class="p">)</span> <span class="k">as</span> <span class="n">record</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="s2">&quot;another warning&quot;</span><span class="p">,</span> <span class="ne">RuntimeWarning</span><span class="p">)</span>

<span class="c1"># check that only one warning was raised</span>
<span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">record</span><span class="p">)</span> <span class="o">==</span> <span class="mi">1</span>
<span class="c1"># check that the message matches</span>
<span class="k">assert</span> <span class="n">record</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">message</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="s2">&quot;another warning&quot;</span>
</pre></div>
</div>
<p>Alternatively, you can examine raised warnings in detail using the
<a class="reference internal" href="#recwarn"><span>recwarn</span></a> fixture (see below).</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last"><code class="docutils literal"><span class="pre">DeprecationWarning</span></code> and <code class="docutils literal"><span class="pre">PendingDeprecationWarning</span></code> are treated
differently; see <a class="reference internal" href="#ensuring-function-triggers"><span>Ensuring a function triggers a deprecation warning</span></a>.</p>
</div>
</div>
<div class="section" id="recording-warnings">
<span id="recwarn"></span><h2>Recording warnings<a class="headerlink" href="#recording-warnings" title="Permalink to this headline"></a></h2>
<p>You can record raised warnings either using <code class="docutils literal"><span class="pre">pytest.warns</span></code> or with
the <code class="docutils literal"><span class="pre">recwarn</span></code> fixture.</p>
<p>To record with <code class="docutils literal"><span class="pre">pytest.warns</span></code> without asserting anything about the warnings,
pass <code class="docutils literal"><span class="pre">None</span></code> as the expected warning type:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">with</span> <span class="n">pytest</span><span class="o">.</span><span class="n">warns</span><span class="p">(</span><span class="bp">None</span><span class="p">)</span> <span class="k">as</span> <span class="n">record</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="s2">&quot;user&quot;</span><span class="p">,</span> <span class="ne">UserWarning</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="s2">&quot;runtime&quot;</span><span class="p">,</span> <span class="ne">RuntimeWarning</span><span class="p">)</span>

<span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">record</span><span class="p">)</span> <span class="o">==</span> <span class="mi">2</span>
<span class="k">assert</span> <span class="nb">str</span><span class="p">(</span><span class="n">record</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">message</span><span class="p">)</span> <span class="o">==</span> <span class="s2">&quot;user&quot;</span>
<span class="k">assert</span> <span class="nb">str</span><span class="p">(</span><span class="n">record</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">message</span><span class="p">)</span> <span class="o">==</span> <span class="s2">&quot;runtime&quot;</span>
</pre></div>
</div>
<p>The <code class="docutils literal"><span class="pre">recwarn</span></code> fixture will record warnings for the whole function:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">warnings</span>

<span class="k">def</span> <span class="nf">test_hello</span><span class="p">(</span><span class="n">recwarn</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="s2">&quot;hello&quot;</span><span class="p">,</span> <span class="ne">UserWarning</span><span class="p">)</span>
    <span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">recwarn</span><span class="p">)</span> <span class="o">==</span> <span class="mi">1</span>
    <span class="n">w</span> <span class="o">=</span> <span class="n">recwarn</span><span class="o">.</span><span class="n">pop</span><span class="p">(</span><span class="ne">UserWarning</span><span class="p">)</span>
    <span class="k">assert</span> <span class="nb">issubclass</span><span class="p">(</span><span class="n">w</span><span class="o">.</span><span class="n">category</span><span class="p">,</span> <span class="ne">UserWarning</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">message</span><span class="p">)</span> <span class="o">==</span> <span class="s2">&quot;hello&quot;</span>
    <span class="k">assert</span> <span class="n">w</span><span class="o">.</span><span class="n">filename</span>
    <span class="k">assert</span> <span class="n">w</span><span class="o">.</span><span class="n">lineno</span>
</pre></div>
</div>
<p>Both <code class="docutils literal"><span class="pre">recwarn</span></code> and <code class="docutils literal"><span class="pre">pytest.warns</span></code> return the same interface for recorded
warnings: a WarningsRecorder instance. To view the recorded warnings, you can
iterate over this instance, call <code class="docutils literal"><span class="pre">len</span></code> on it to get the number of recorded
warnings, or index into it to get a particular recorded warning. It also
provides these methods:</p>
<dl class="class">
<dt id="_pytest.recwarn.WarningsRecorder">
<em class="property">class </em><code class="descname">WarningsRecorder</code><a class="reference internal" href="_modules/_pytest/recwarn.html#WarningsRecorder"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.recwarn.WarningsRecorder" title="Permalink to this definition"></a></dt>
<dd><p>A context manager to record raised warnings.</p>
<p>Adapted from <cite>warnings.catch_warnings</cite>.</p>
<dl class="attribute">
<dt id="_pytest.recwarn.WarningsRecorder.list">
<code class="descname">list</code><a class="headerlink" href="#_pytest.recwarn.WarningsRecorder.list" title="Permalink to this definition"></a></dt>
<dd><p>The list of recorded warnings.</p>
</dd></dl>

<dl class="method">
<dt id="_pytest.recwarn.WarningsRecorder.pop">
<code class="descname">pop</code><span class="sig-paren">(</span><em>cls=&lt;type 'exceptions.Warning'&gt;</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/_pytest/recwarn.html#WarningsRecorder.pop"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.recwarn.WarningsRecorder.pop" title="Permalink to this definition"></a></dt>
<dd><p>Pop the first recorded warning, raise exception if not exists.</p>
</dd></dl>

<dl class="method">
<dt id="_pytest.recwarn.WarningsRecorder.clear">
<code class="descname">clear</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="reference internal" href="_modules/_pytest/recwarn.html#WarningsRecorder.clear"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#_pytest.recwarn.WarningsRecorder.clear" title="Permalink to this definition"></a></dt>
<dd><p>Clear the list of recorded warnings.</p>
</dd></dl>

</dd></dl>

<p>Each recorded warning has the attributes <code class="docutils literal"><span class="pre">message</span></code>, <code class="docutils literal"><span class="pre">category</span></code>,
<code class="docutils literal"><span class="pre">filename</span></code>, <code class="docutils literal"><span class="pre">lineno</span></code>, <code class="docutils literal"><span class="pre">file</span></code>, and <code class="docutils literal"><span class="pre">line</span></code>. The <code class="docutils literal"><span class="pre">category</span></code> is the
class of the warning. The <code class="docutils literal"><span class="pre">message</span></code> is the warning itself; calling
<code class="docutils literal"><span class="pre">str(message)</span></code> will return the actual message of the warning.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last"><code class="docutils literal"><span class="pre">DeprecationWarning</span></code> and <code class="docutils literal"><span class="pre">PendingDeprecationWarning</span></code> are treated
differently; see <a class="reference internal" href="#ensuring-function-triggers"><span>Ensuring a function triggers a deprecation warning</span></a>.</p>
</div>
</div>
<div class="section" id="ensuring-a-function-triggers-a-deprecation-warning">
<span id="ensuring-function-triggers"></span><h2>Ensuring a function triggers a deprecation warning<a class="headerlink" href="#ensuring-a-function-triggers-a-deprecation-warning" title="Permalink to this headline"></a></h2>
<p>You can also call a global helper for checking
that a certain function call triggers a <code class="docutils literal"><span class="pre">DeprecationWarning</span></code> or
<code class="docutils literal"><span class="pre">PendingDeprecationWarning</span></code>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">pytest</span>

<span class="k">def</span> <span class="nf">test_global</span><span class="p">():</span>
    <span class="n">pytest</span><span class="o">.</span><span class="n">deprecated_call</span><span class="p">(</span><span class="n">myfunction</span><span class="p">,</span> <span class="mi">17</span><span class="p">)</span>
</pre></div>
</div>
<p>By default, <code class="docutils literal"><span class="pre">DeprecationWarning</span></code> and <code class="docutils literal"><span class="pre">PendingDeprecationWarning</span></code> will not be
caught when using <code class="docutils literal"><span class="pre">pytest.warns</span></code> or <code class="docutils literal"><span class="pre">recwarn</span></code> because default Python warnings filters hide
them. If you wish to record them in your own code, use the
command <code class="docutils literal"><span class="pre">warnings.simplefilter('always')</span></code>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">warnings</span>
<span class="kn">import</span> <span class="nn">pytest</span>

<span class="k">def</span> <span class="nf">test_deprecation</span><span class="p">(</span><span class="n">recwarn</span><span class="p">):</span>
    <span class="n">warnings</span><span class="o">.</span><span class="n">simplefilter</span><span class="p">(</span><span class="s1">&#39;always&#39;</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="s2">&quot;deprecated&quot;</span><span class="p">,</span> <span class="ne">DeprecationWarning</span><span class="p">)</span>
    <span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">recwarn</span><span class="p">)</span> <span class="o">==</span> <span class="mi">1</span>
    <span class="k">assert</span> <span class="n">recwarn</span><span class="o">.</span><span class="n">pop</span><span class="p">(</span><span class="ne">DeprecationWarning</span><span class="p">)</span>
</pre></div>
</div>
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<li><a class="reference internal" href="#recording-warnings">Recording warnings</a></li>
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