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<div class="section" id="testing-flask-applications">
<span id="testing"></span><h1>Testing Flask Applications<a class="headerlink" href="#testing-flask-applications" title="Permalink to this headline">¶</a></h1>
<blockquote>
<div><strong>Something that is untested is broken.</strong></div></blockquote>
<p>The origin of this quote is unknown and while it is not entirely correct, it is also
not far from the truth. Untested applications make it hard to
improve existing code and developers of untested applications tend to
become pretty paranoid. If an application has automated tests, you can
safely make changes and instantly know if anything breaks.</p>
<p>Flask provides a way to test your application by exposing the Werkzeug
test <a class="reference external" href="http://werkzeug.pocoo.org/docs/test/#werkzeug.test.Client" title="(in Werkzeug v0.7)"><tt class="xref py py-class docutils literal"><span class="pre">Client</span></tt></a> and handling the context locals for you.
You can then use that with your favourite testing solution. In this documentation
we will use the <a class="reference external" href="http://docs.python.org/dev/library/unittest.html#unittest" title="(in Python v3.3)"><tt class="xref py py-mod docutils literal"><span class="pre">unittest</span></tt></a> package that comes pre-installed with Python.</p>
<div class="section" id="the-application">
<h2>The Application<a class="headerlink" href="#the-application" title="Permalink to this headline">¶</a></h2>
<p>First, we need an application to test; we will use the application from
the <a class="reference internal" href="tutorial/index.html#tutorial"><em>Tutorial</em></a>. If you don’t have that application yet, get the
sources from <a class="reference external" href="http://github.com/mitsuhiko/flask/tree/master/examples/flaskr/">the examples</a>.</p>
</div>
<div class="section" id="the-testing-skeleton">
<h2>The Testing Skeleton<a class="headerlink" href="#the-testing-skeleton" title="Permalink to this headline">¶</a></h2>
<p>In order to test the application, we add a second module
(<cite>flaskr_tests.py</cite>) and create a unittest skeleton there:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">os</span>
<span class="kn">import</span> <span class="nn">flaskr</span>
<span class="kn">import</span> <span class="nn">unittest</span>
<span class="kn">import</span> <span class="nn">tempfile</span>
<span class="k">class</span> <span class="nc">FlaskrTestCase</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="k">def</span> <span class="nf">setUp</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">db_fd</span><span class="p">,</span> <span class="n">flaskr</span><span class="o">.</span><span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="p">[</span><span class="s">'DATABASE'</span><span class="p">]</span> <span class="o">=</span> <span class="n">tempfile</span><span class="o">.</span><span class="n">mkstemp</span><span class="p">()</span>
<span class="n">flaskr</span><span class="o">.</span><span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="p">[</span><span class="s">'TESTING'</span><span class="p">]</span> <span class="o">=</span> <span class="bp">True</span>
<span class="bp">self</span><span class="o">.</span><span class="n">app</span> <span class="o">=</span> <span class="n">flaskr</span><span class="o">.</span><span class="n">app</span><span class="o">.</span><span class="n">test_client</span><span class="p">()</span>
<span class="n">flaskr</span><span class="o">.</span><span class="n">init_db</span><span class="p">()</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="n">os</span><span class="o">.</span><span class="n">close</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">db_fd</span><span class="p">)</span>
<span class="n">os</span><span class="o">.</span><span class="n">unlink</span><span class="p">(</span><span class="n">flaskr</span><span class="o">.</span><span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="p">[</span><span class="s">'DATABASE'</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">unittest</span><span class="o">.</span><span class="n">main</span><span class="p">()</span>
</pre></div>
</div>
<p>The code in the <a class="reference external" href="http://docs.python.org/dev/library/unittest.html#unittest.TestCase.setUp" title="(in Python v3.3)"><tt class="xref py py-meth docutils literal"><span class="pre">setUp()</span></tt></a> method creates a new test
client and initializes a new database. This function is called before
each individual test function is run. To delete the database after the
test, we close the file and remove it from the filesystem in the
<a class="reference external" href="http://docs.python.org/dev/library/unittest.html#unittest.TestCase.tearDown" title="(in Python v3.3)"><tt class="xref py py-meth docutils literal"><span class="pre">tearDown()</span></tt></a> method. Additionally during setup the
<tt class="docutils literal"><span class="pre">TESTING</span></tt> config flag is activated. What it does is disabling the error
catching during request handling so that you get better error reports when
performing test requests against the application.</p>
<p>This test client will give us a simple interface to the application. We can
trigger test requests to the application, and the client will also keep track
of cookies for us.</p>
<p>Because SQLite3 is filesystem-based we can easily use the tempfile module
to create a temporary database and initialize it. The
<a class="reference external" href="http://docs.python.org/dev/library/tempfile.html#tempfile.mkstemp" title="(in Python v3.3)"><tt class="xref py py-func docutils literal"><span class="pre">mkstemp()</span></tt></a> function does two things for us: it returns a
low-level file handle and a random file name, the latter we use as
database name. We just have to keep the <cite>db_fd</cite> around so that we can use
the <a class="reference external" href="http://docs.python.org/dev/library/os.html#os.close" title="(in Python v3.3)"><tt class="xref py py-func docutils literal"><span class="pre">os.close()</span></tt></a> function to close the file.</p>
<p>If we now run the test suite, we should see the following output:</p>
<div class="highlight-python"><pre>$ python flaskr_tests.py
----------------------------------------------------------------------
Ran 0 tests in 0.000s
OK</pre>
</div>
<p>Even though it did not run any actual tests, we already know that our flaskr
application is syntactically valid, otherwise the import would have died
with an exception.</p>
</div>
<div class="section" id="the-first-test">
<h2>The First Test<a class="headerlink" href="#the-first-test" title="Permalink to this headline">¶</a></h2>
<p>Now it’s time to start testing the functionality of the application.
Let’s check that the application shows “No entries here so far” if we
access the root of the application (<tt class="docutils literal"><span class="pre">/</span></tt>). To do this, we add a new
test method to our class, like this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">FlaskrTestCase</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="k">def</span> <span class="nf">setUp</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">db_fd</span><span class="p">,</span> <span class="n">flaskr</span><span class="o">.</span><span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="p">[</span><span class="s">'DATABASE'</span><span class="p">]</span> <span class="o">=</span> <span class="n">tempfile</span><span class="o">.</span><span class="n">mkstemp</span><span class="p">()</span>
<span class="bp">self</span><span class="o">.</span><span class="n">app</span> <span class="o">=</span> <span class="n">flaskr</span><span class="o">.</span><span class="n">app</span><span class="o">.</span><span class="n">test_client</span><span class="p">()</span>
<span class="n">flaskr</span><span class="o">.</span><span class="n">init_db</span><span class="p">()</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="n">os</span><span class="o">.</span><span class="n">close</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">db_fd</span><span class="p">)</span>
<span class="n">os</span><span class="o">.</span><span class="n">unlink</span><span class="p">(</span><span class="n">flaskr</span><span class="o">.</span><span class="n">DATABASE</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">test_empty_db</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="n">rv</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">app</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s">'/'</span><span class="p">)</span>
<span class="k">assert</span> <span class="s">'No entries here so far'</span> <span class="ow">in</span> <span class="n">rv</span><span class="o">.</span><span class="n">data</span>
</pre></div>
</div>
<p>Notice that our test functions begin with the word <cite>test</cite>; this allows
<a class="reference external" href="http://docs.python.org/dev/library/unittest.html#unittest" title="(in Python v3.3)"><tt class="xref py py-mod docutils literal"><span class="pre">unittest</span></tt></a> to automatically identify the method as a test to run.</p>
<p>By using <cite>self.app.get</cite> we can send an HTTP <cite>GET</cite> request to the application with
the given path. The return value will be a <a class="reference internal" href="api.html#flask.Flask.response_class" title="flask.Flask.response_class"><tt class="xref py py-class docutils literal"><span class="pre">response_class</span></tt></a> object.
We can now use the <a class="reference external" href="http://werkzeug.pocoo.org/docs/wrappers/#werkzeug.wrappers.BaseResponse.data" title="(in Werkzeug v0.7)"><tt class="xref py py-attr docutils literal"><span class="pre">data</span></tt></a> attribute to inspect
the return value (as string) from the application. In this case, we ensure that
<tt class="docutils literal"><span class="pre">'No</span> <span class="pre">entries</span> <span class="pre">here</span> <span class="pre">so</span> <span class="pre">far'</span></tt> is part of the output.</p>
<p>Run it again and you should see one passing test:</p>
<div class="highlight-python"><pre>$ python flaskr_tests.py
.
----------------------------------------------------------------------
Ran 1 test in 0.034s
OK</pre>
</div>
</div>
<div class="section" id="logging-in-and-out">
<h2>Logging In and Out<a class="headerlink" href="#logging-in-and-out" title="Permalink to this headline">¶</a></h2>
<p>The majority of the functionality of our application is only available for
the administrative user, so we need a way to log our test client in and out
of the application. To do this, we fire some requests to the login and logout
pages with the required form data (username and password). And because the
login and logout pages redirect, we tell the client to <cite>follow_redirects</cite>.</p>
<p>Add the following two methods to your <cite>FlaskrTestCase</cite> class:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">login</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">username</span><span class="p">,</span> <span class="n">password</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">app</span><span class="o">.</span><span class="n">post</span><span class="p">(</span><span class="s">'/login'</span><span class="p">,</span> <span class="n">data</span><span class="o">=</span><span class="nb">dict</span><span class="p">(</span>
<span class="n">username</span><span class="o">=</span><span class="n">username</span><span class="p">,</span>
<span class="n">password</span><span class="o">=</span><span class="n">password</span>
<span class="p">),</span> <span class="n">follow_redirects</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">logout</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">app</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s">'/logout'</span><span class="p">,</span> <span class="n">follow_redirects</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
</pre></div>
</div>
<p>Now we can easily test that logging in and out works and that it fails with
invalid credentials. Add this new test to the class:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">test_login_logout</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="n">rv</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">login</span><span class="p">(</span><span class="s">'admin'</span><span class="p">,</span> <span class="s">'default'</span><span class="p">)</span>
<span class="k">assert</span> <span class="s">'You were logged in'</span> <span class="ow">in</span> <span class="n">rv</span><span class="o">.</span><span class="n">data</span>
<span class="n">rv</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">logout</span><span class="p">()</span>
<span class="k">assert</span> <span class="s">'You were logged out'</span> <span class="ow">in</span> <span class="n">rv</span><span class="o">.</span><span class="n">data</span>
<span class="n">rv</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">login</span><span class="p">(</span><span class="s">'adminx'</span><span class="p">,</span> <span class="s">'default'</span><span class="p">)</span>
<span class="k">assert</span> <span class="s">'Invalid username'</span> <span class="ow">in</span> <span class="n">rv</span><span class="o">.</span><span class="n">data</span>
<span class="n">rv</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">login</span><span class="p">(</span><span class="s">'admin'</span><span class="p">,</span> <span class="s">'defaultx'</span><span class="p">)</span>
<span class="k">assert</span> <span class="s">'Invalid password'</span> <span class="ow">in</span> <span class="n">rv</span><span class="o">.</span><span class="n">data</span>
</pre></div>
</div>
</div>
<div class="section" id="test-adding-messages">
<h2>Test Adding Messages<a class="headerlink" href="#test-adding-messages" title="Permalink to this headline">¶</a></h2>
<p>We should also test that adding messages works. Add a new test method
like this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">test_messages</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">login</span><span class="p">(</span><span class="s">'admin'</span><span class="p">,</span> <span class="s">'default'</span><span class="p">)</span>
<span class="n">rv</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">app</span><span class="o">.</span><span class="n">post</span><span class="p">(</span><span class="s">'/add'</span><span class="p">,</span> <span class="n">data</span><span class="o">=</span><span class="nb">dict</span><span class="p">(</span>
<span class="n">title</span><span class="o">=</span><span class="s">'<Hello>'</span><span class="p">,</span>
<span class="n">text</span><span class="o">=</span><span class="s">'<strong>HTML</strong> allowed here'</span>
<span class="p">),</span> <span class="n">follow_redirects</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="k">assert</span> <span class="s">'No entries here so far'</span> <span class="ow">not</span> <span class="ow">in</span> <span class="n">rv</span><span class="o">.</span><span class="n">data</span>
<span class="k">assert</span> <span class="s">'&lt;Hello&gt;'</span> <span class="ow">in</span> <span class="n">rv</span><span class="o">.</span><span class="n">data</span>
<span class="k">assert</span> <span class="s">'<strong>HTML</strong> allowed here'</span> <span class="ow">in</span> <span class="n">rv</span><span class="o">.</span><span class="n">data</span>
</pre></div>
</div>
<p>Here we check that HTML is allowed in the text but not in the title,
which is the intended behavior.</p>
<p>Running that should now give us three passing tests:</p>
<div class="highlight-python"><pre>$ python flaskr_tests.py
...
----------------------------------------------------------------------
Ran 3 tests in 0.332s
OK</pre>
</div>
<p>For more complex tests with headers and status codes, check out the
<a class="reference external" href="http://github.com/mitsuhiko/flask/tree/master/examples/minitwit/">MiniTwit Example</a> from the sources which contains a larger test
suite.</p>
</div>
<div class="section" id="other-testing-tricks">
<h2>Other Testing Tricks<a class="headerlink" href="#other-testing-tricks" title="Permalink to this headline">¶</a></h2>
<p>Besides using the test client as shown above, there is also the
<a class="reference internal" href="api.html#flask.Flask.test_request_context" title="flask.Flask.test_request_context"><tt class="xref py py-meth docutils literal"><span class="pre">test_request_context()</span></tt></a> method that can be used
in combination with the <cite>with</cite> statement to activate a request context
temporarily. With this you can access the <a class="reference internal" href="api.html#flask.request" title="flask.request"><tt class="xref py py-class docutils literal"><span class="pre">request</span></tt></a>,
<a class="reference internal" href="api.html#flask.g" title="flask.g"><tt class="xref py py-class docutils literal"><span class="pre">g</span></tt></a> and <a class="reference internal" href="api.html#flask.session" title="flask.session"><tt class="xref py py-class docutils literal"><span class="pre">session</span></tt></a> objects like in view
functions. Here is a full example that demonstrates this approach:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span> <span class="o">=</span> <span class="n">flask</span><span class="o">.</span><span class="n">Flask</span><span class="p">(</span><span class="n">__name__</span><span class="p">)</span>
<span class="k">with</span> <span class="n">app</span><span class="o">.</span><span class="n">test_request_context</span><span class="p">(</span><span class="s">'/?name=Peter'</span><span class="p">):</span>
<span class="k">assert</span> <span class="n">flask</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">path</span> <span class="o">==</span> <span class="s">'/'</span>
<span class="k">assert</span> <span class="n">flask</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">args</span><span class="p">[</span><span class="s">'name'</span><span class="p">]</span> <span class="o">==</span> <span class="s">'Peter'</span>
</pre></div>
</div>
<p>All the other objects that are context bound can be used in the same
way.</p>
<p>If you want to test your application with different configurations and
there does not seem to be a good way to do that, consider switching to
application factories (see <a class="reference internal" href="patterns/appfactories.html#app-factories"><em>Application Factories</em></a>).</p>
<p>Note however that if you are using a test request context, the
<a class="reference internal" href="api.html#flask.Flask.before_request" title="flask.Flask.before_request"><tt class="xref py py-meth docutils literal"><span class="pre">before_request()</span></tt></a> functions are not automatically called
same for <a class="reference internal" href="api.html#flask.Flask.after_request" title="flask.Flask.after_request"><tt class="xref py py-meth docutils literal"><span class="pre">after_request()</span></tt></a> functions. However
<a class="reference internal" href="api.html#flask.Flask.teardown_request" title="flask.Flask.teardown_request"><tt class="xref py py-meth docutils literal"><span class="pre">teardown_request()</span></tt></a> functions are indeed executed when
the test request context leaves the <cite>with</cite> block. If you do want the
<a class="reference internal" href="api.html#flask.Flask.before_request" title="flask.Flask.before_request"><tt class="xref py py-meth docutils literal"><span class="pre">before_request()</span></tt></a> functions to be called as well, you
need to call <a class="reference internal" href="api.html#flask.Flask.preprocess_request" title="flask.Flask.preprocess_request"><tt class="xref py py-meth docutils literal"><span class="pre">preprocess_request()</span></tt></a> yourself:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span> <span class="o">=</span> <span class="n">flask</span><span class="o">.</span><span class="n">Flask</span><span class="p">(</span><span class="n">__name__</span><span class="p">)</span>
<span class="k">with</span> <span class="n">app</span><span class="o">.</span><span class="n">test_request_context</span><span class="p">(</span><span class="s">'/?name=Peter'</span><span class="p">):</span>
<span class="n">app</span><span class="o">.</span><span class="n">preprocess_request</span><span class="p">()</span>
<span class="o">...</span>
</pre></div>
</div>
<p>This can be necessary to open database connections or something similar
depending on how your application was designed.</p>
<p>If you want to call the <a class="reference internal" href="api.html#flask.Flask.after_request" title="flask.Flask.after_request"><tt class="xref py py-meth docutils literal"><span class="pre">after_request()</span></tt></a> functions you
need to call into <a class="reference internal" href="api.html#flask.Flask.process_response" title="flask.Flask.process_response"><tt class="xref py py-meth docutils literal"><span class="pre">process_response()</span></tt></a> which however
requires that you pass it a response object:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span> <span class="o">=</span> <span class="n">flask</span><span class="o">.</span><span class="n">Flask</span><span class="p">(</span><span class="n">__name__</span><span class="p">)</span>
<span class="k">with</span> <span class="n">app</span><span class="o">.</span><span class="n">test_request_context</span><span class="p">(</span><span class="s">'/?name=Peter'</span><span class="p">):</span>
<span class="n">resp</span> <span class="o">=</span> <span class="n">Response</span><span class="p">(</span><span class="s">'...'</span><span class="p">)</span>
<span class="n">resp</span> <span class="o">=</span> <span class="n">app</span><span class="o">.</span><span class="n">process_response</span><span class="p">(</span><span class="n">resp</span><span class="p">)</span>
<span class="o">...</span>
</pre></div>
</div>
<p>This in general is less useful because at that point you can directly
start using the test client.</p>
</div>
<div class="section" id="keeping-the-context-around">
<h2>Keeping the Context Around<a class="headerlink" href="#keeping-the-context-around" title="Permalink to this headline">¶</a></h2>
<p class="versionadded">
<span class="versionmodified">New in version 0.4.</span></p>
<p>Sometimes it is helpful to trigger a regular request but still keep the
context around for a little longer so that additional introspection can
happen. With Flask 0.4 this is possible by using the
<a class="reference internal" href="api.html#flask.Flask.test_client" title="flask.Flask.test_client"><tt class="xref py py-meth docutils literal"><span class="pre">test_client()</span></tt></a> with a <cite>with</cite> block:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span> <span class="o">=</span> <span class="n">flask</span><span class="o">.</span><span class="n">Flask</span><span class="p">(</span><span class="n">__name__</span><span class="p">)</span>
<span class="k">with</span> <span class="n">app</span><span class="o">.</span><span class="n">test_client</span><span class="p">()</span> <span class="k">as</span> <span class="n">c</span><span class="p">:</span>
<span class="n">rv</span> <span class="o">=</span> <span class="n">c</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s">'/?tequila=42'</span><span class="p">)</span>
<span class="k">assert</span> <span class="n">request</span><span class="o">.</span><span class="n">args</span><span class="p">[</span><span class="s">'tequila'</span><span class="p">]</span> <span class="o">==</span> <span class="s">'42'</span>
</pre></div>
</div>
<p>If you were to use just the <a class="reference internal" href="api.html#flask.Flask.test_client" title="flask.Flask.test_client"><tt class="xref py py-meth docutils literal"><span class="pre">test_client()</span></tt></a> without
the <cite>with</cite> block, the <cite>assert</cite> would fail with an error because <cite>request</cite>
is no longer available (because you are trying to use it outside of the actual request).
However, keep in mind that any <a class="reference internal" href="api.html#flask.Flask.after_request" title="flask.Flask.after_request"><tt class="xref py py-meth docutils literal"><span class="pre">after_request()</span></tt></a> functions
are already called at this point so your database connection and
everything involved is probably already closed down.</p>
</div>
<div class="section" id="accessing-and-modifying-sessions">
<h2>Accessing and Modifying Sessions<a class="headerlink" href="#accessing-and-modifying-sessions" title="Permalink to this headline">¶</a></h2>
<p class="versionadded">
<span class="versionmodified">New in version 0.8.</span></p>
<p>Sometimes it can be very helpful to access or modify the sessions from the
test client. Generally there are two ways for this. If you just want to
ensure that a session has certain keys set to certain values you can just
keep the context around and access <a class="reference internal" href="api.html#flask.session" title="flask.session"><tt class="xref py py-data docutils literal"><span class="pre">flask.session</span></tt></a>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">with</span> <span class="n">app</span><span class="o">.</span><span class="n">test_client</span><span class="p">()</span> <span class="k">as</span> <span class="n">c</span><span class="p">:</span>
<span class="n">rv</span> <span class="o">=</span> <span class="n">c</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s">'/'</span><span class="p">)</span>
<span class="k">assert</span> <span class="n">flask</span><span class="o">.</span><span class="n">session</span><span class="p">[</span><span class="s">'foo'</span><span class="p">]</span> <span class="o">==</span> <span class="mi">42</span>
</pre></div>
</div>
<p>This however does not make it possible to also modify the session or to
access the session before a request was fired. Starting with Flask 0.8 we
provide a so called “session transaction” which simulates the appropriate
calls to open a session in the context of the test client and to modify
it. At the end of the transaction the session is stored. This works
independently of the session backend used:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">with</span> <span class="n">app</span><span class="o">.</span><span class="n">test_client</span><span class="p">()</span> <span class="k">as</span> <span class="n">c</span><span class="p">:</span>
<span class="k">with</span> <span class="n">c</span><span class="o">.</span><span class="n">session_transaction</span><span class="p">()</span> <span class="k">as</span> <span class="n">sess</span><span class="p">:</span>
<span class="n">sess</span><span class="p">[</span><span class="s">'a_key'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'a value'</span>
<span class="c"># once this is reached the session was stored</span>
</pre></div>
</div>
<p>Note that in this case you have to use the <tt class="docutils literal"><span class="pre">sess</span></tt> object instead of the
<a class="reference internal" href="api.html#flask.session" title="flask.session"><tt class="xref py py-data docutils literal"><span class="pre">flask.session</span></tt></a> proxy. The object however itself will provide the
same interface.</p>
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<h3><a href="index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Testing Flask Applications</a><ul>
<li><a class="reference internal" href="#the-application">The Application</a></li>
<li><a class="reference internal" href="#the-testing-skeleton">The Testing Skeleton</a></li>
<li><a class="reference internal" href="#the-first-test">The First Test</a></li>
<li><a class="reference internal" href="#logging-in-and-out">Logging In and Out</a></li>
<li><a class="reference internal" href="#test-adding-messages">Test Adding Messages</a></li>
<li><a class="reference internal" href="#other-testing-tricks">Other Testing Tricks</a></li>
<li><a class="reference internal" href="#keeping-the-context-around">Keeping the Context Around</a></li>
<li><a class="reference internal" href="#accessing-and-modifying-sessions">Accessing and Modifying Sessions</a></li>
</ul>
</li>
</ul>
<h3>Related Topics</h3>
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<li><a href="index.html">Documentation overview</a><ul>
<li>Previous: <a href="templating.html" title="previous chapter">Templates</a></li>
<li>Next: <a href="errorhandling.html" title="next chapter">Handling Application Errors</a></li>
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