=============
Testing tools
=============

.. currentmodule:: django.test

Django provides a small set of tools that come in handy when writing tests.

.. _test-client:

The test client
===============

The test client is a Python class that acts as a dummy Web browser, allowing
you to test your views and interact with your Django-powered application
programmatically.

Some of the things you can do with the test client are:

* Simulate GET and POST requests on a URL and observe the response --
  everything from low-level HTTP (result headers and status codes) to
  page content.

* See the chain of redirects (if any) and check the URL and status code at
  each step.

* Test that a given request is rendered by a given Django template, with
  a template context that contains certain values.

Note that the test client is not intended to be a replacement for Selenium_ or
other "in-browser" frameworks. Django's test client has a different focus. In
short:

* Use Django's test client to establish that the correct template is being
  rendered and that the template is passed the correct context data.

* Use in-browser frameworks like Selenium_ to test *rendered* HTML and the
  *behavior* of Web pages, namely JavaScript functionality. Django also
  provides special support for those frameworks; see the section on
  :class:`~django.test.LiveServerTestCase` for more details.

A comprehensive test suite should use a combination of both test types.

Overview and a quick example
----------------------------

To use the test client, instantiate ``django.test.Client`` and retrieve
Web pages::

    >>> from django.test import Client
    >>> c = Client()
    >>> response = c.post('/login/', {'username': 'john', 'password': 'smith'})
    >>> response.status_code
    200
    >>> response = c.get('/customer/details/')
    >>> response.content
    b'<!DOCTYPE html...'

As this example suggests, you can instantiate ``Client`` from within a session
of the Python interactive interpreter.

Note a few important things about how the test client works:

* The test client does *not* require the Web server to be running. In fact,
  it will run just fine with no Web server running at all! That's because
  it avoids the overhead of HTTP and deals directly with the Django
  framework. This helps make the unit tests run quickly.

* When retrieving pages, remember to specify the *path* of the URL, not the
  whole domain. For example, this is correct::

      >>> c.get('/login/')

  This is incorrect::

      >>> c.get('https://www.example.com/login/')

  The test client is not capable of retrieving Web pages that are not
  powered by your Django project. If you need to retrieve other Web pages,
  use a Python standard library module such as :mod:`urllib`.

* To resolve URLs, the test client uses whatever URLconf is pointed-to by
  your :setting:`ROOT_URLCONF` setting.

* Although the above example would work in the Python interactive
  interpreter, some of the test client's functionality, notably the
  template-related functionality, is only available *while tests are
  running*.

  The reason for this is that Django's test runner performs a bit of black
  magic in order to determine which template was loaded by a given view.
  This black magic (essentially a patching of Django's template system in
  memory) only happens during test running.

* By default, the test client will disable any CSRF checks
  performed by your site.

  If, for some reason, you *want* the test client to perform CSRF
  checks, you can create an instance of the test client that
  enforces CSRF checks. To do this, pass in the
  ``enforce_csrf_checks`` argument when you construct your
  client::

      >>> from django.test import Client
      >>> csrf_client = Client(enforce_csrf_checks=True)

Making requests
---------------

Use the ``django.test.Client`` class to make requests.

.. class:: Client(enforce_csrf_checks=False, json_encoder=DjangoJSONEncoder, **defaults)

    It requires no arguments at time of construction. However, you can use
    keyword arguments to specify some default headers. For example, this will
    send a ``User-Agent`` HTTP header in each request::

        >>> c = Client(HTTP_USER_AGENT='Mozilla/5.0')

    The values from the ``extra`` keyword arguments passed to
    :meth:`~django.test.Client.get()`,
    :meth:`~django.test.Client.post()`, etc. have precedence over
    the defaults passed to the class constructor.

    The ``enforce_csrf_checks`` argument can be used to test CSRF
    protection (see above).

    The ``json_encoder`` argument allows setting a custom JSON encoder for
    the JSON serialization that's described in :meth:`post`.

    The ``raise_request_exception`` argument allows controlling whether or not
    exceptions raised during the request should also be raised in the test.
    Defaults to ``True``.

    Once you have a ``Client`` instance, you can call any of the following
    methods:

    .. method:: Client.get(path, data=None, follow=False, secure=False, **extra)

        Makes a GET request on the provided ``path`` and returns a ``Response``
        object, which is documented below.

        The key-value pairs in the ``data`` dictionary are used to create a GET
        data payload. For example::

            >>> c = Client()
            >>> c.get('/customers/details/', {'name': 'fred', 'age': 7})

        ...will result in the evaluation of a GET request equivalent to::

            /customers/details/?name=fred&age=7

        The ``extra`` keyword arguments parameter can be used to specify
        headers to be sent in the request. For example::

            >>> c = Client()
            >>> c.get('/customers/details/', {'name': 'fred', 'age': 7},
            ...       HTTP_ACCEPT='application/json')

        ...will send the HTTP header ``HTTP_ACCEPT`` to the details view, which
        is a good way to test code paths that use the
        :meth:`django.http.HttpRequest.accepts()` method.

        .. admonition:: CGI specification

            The headers sent via ``**extra`` should follow CGI_ specification.
            For example, emulating a different "Host" header as sent in the
            HTTP request from the browser to the server should be passed
            as ``HTTP_HOST``.

            .. _CGI: https://www.w3.org/CGI/

        If you already have the GET arguments in URL-encoded form, you can
        use that encoding instead of using the data argument. For example,
        the previous GET request could also be posed as::

        >>> c = Client()
        >>> c.get('/customers/details/?name=fred&age=7')

        If you provide a URL with both an encoded GET data and a data argument,
        the data argument will take precedence.

        If you set ``follow`` to ``True`` the client will follow any redirects
        and a ``redirect_chain`` attribute will be set in the response object
        containing tuples of the intermediate urls and status codes.

        If you had a URL ``/redirect_me/`` that redirected to ``/next/``, that
        redirected to ``/final/``, this is what you'd see::

            >>> response = c.get('/redirect_me/', follow=True)
            >>> response.redirect_chain
            [('http://testserver/next/', 302), ('http://testserver/final/', 302)]

        If you set ``secure`` to ``True`` the client will emulate an HTTPS
        request.

    .. method:: Client.post(path, data=None, content_type=MULTIPART_CONTENT, follow=False, secure=False, **extra)

        Makes a POST request on the provided ``path`` and returns a
        ``Response`` object, which is documented below.

        The key-value pairs in the ``data`` dictionary are used to submit POST
        data. For example::

            >>> c = Client()
            >>> c.post('/login/', {'name': 'fred', 'passwd': 'secret'})

        ...will result in the evaluation of a POST request to this URL::

            /login/

        ...with this POST data::

            name=fred&passwd=secret

        If you provide ``content_type`` as :mimetype:`application/json`, the
        ``data`` is serialized using :func:`json.dumps` if it's a dict, list,
        or tuple. Serialization is performed with
        :class:`~django.core.serializers.json.DjangoJSONEncoder` by default,
        and can be overridden by providing a ``json_encoder`` argument to
        :class:`Client`. This serialization also happens for :meth:`put`,
        :meth:`patch`, and :meth:`delete` requests.

        If you provide any other ``content_type`` (e.g. :mimetype:`text/xml`
        for an XML payload), the contents of ``data`` are sent as-is in the
        POST request, using ``content_type`` in the HTTP ``Content-Type``
        header.

        If you don't provide a value for ``content_type``, the values in
        ``data`` will be transmitted with a content type of
        :mimetype:`multipart/form-data`. In this case, the key-value pairs in
        ``data`` will be encoded as a multipart message and used to create the
        POST data payload.

        To submit multiple values for a given key -- for example, to specify
        the selections for a ``<select multiple>`` -- provide the values as a
        list or tuple for the required key. For example, this value of ``data``
        would submit three selected values for the field named ``choices``::

            {'choices': ('a', 'b', 'd')}

        Submitting files is a special case. To POST a file, you need only
        provide the file field name as a key, and a file handle to the file you
        wish to upload as a value. For example::

            >>> c = Client()
            >>> with open('wishlist.doc', 'rb') as fp:
            ...     c.post('/customers/wishes/', {'name': 'fred', 'attachment': fp})

        (The name ``attachment`` here is not relevant; use whatever name your
        file-processing code expects.)

        You may also provide any file-like object (e.g., :class:`~io.StringIO` or
        :class:`~io.BytesIO`) as a file handle. If you're uploading to an
        :class:`~django.db.models.ImageField`, the object needs a ``name``
        attribute that passes the
        :data:`~django.core.validators.validate_image_file_extension` validator.
        For example::

            >>> from io import BytesIO
            >>> img = BytesIO(b'mybinarydata')
            >>> img.name = 'myimage.jpg'

        Note that if you wish to use the same file handle for multiple
        ``post()`` calls then you will need to manually reset the file
        pointer between posts. The easiest way to do this is to
        manually close the file after it has been provided to
        ``post()``, as demonstrated above.

        You should also ensure that the file is opened in a way that
        allows the data to be read. If your file contains binary data
        such as an image, this means you will need to open the file in
        ``rb`` (read binary) mode.

        The ``extra`` argument acts the same as for :meth:`Client.get`.

        If the URL you request with a POST contains encoded parameters, these
        parameters will be made available in the request.GET data. For example,
        if you were to make the request::

        >>> c.post('/login/?visitor=true', {'name': 'fred', 'passwd': 'secret'})

        ... the view handling this request could interrogate request.POST
        to retrieve the username and password, and could interrogate request.GET
        to determine if the user was a visitor.

        If you set ``follow`` to ``True`` the client will follow any redirects
        and a ``redirect_chain`` attribute will be set in the response object
        containing tuples of the intermediate urls and status codes.

        If you set ``secure`` to ``True`` the client will emulate an HTTPS
        request.

    .. method:: Client.head(path, data=None, follow=False, secure=False, **extra)

        Makes a HEAD request on the provided ``path`` and returns a
        ``Response`` object. This method works just like :meth:`Client.get`,
        including the ``follow``, ``secure`` and ``extra`` arguments, except
        it does not return a message body.

    .. method:: Client.options(path, data='', content_type='application/octet-stream', follow=False, secure=False, **extra)

        Makes an OPTIONS request on the provided ``path`` and returns a
        ``Response`` object. Useful for testing RESTful interfaces.

        When ``data`` is provided, it is used as the request body, and
        a ``Content-Type`` header is set to ``content_type``.

        The ``follow``, ``secure`` and ``extra`` arguments act the same as for
        :meth:`Client.get`.

    .. method:: Client.put(path, data='', content_type='application/octet-stream', follow=False, secure=False, **extra)

        Makes a PUT request on the provided ``path`` and returns a
        ``Response`` object. Useful for testing RESTful interfaces.

        When ``data`` is provided, it is used as the request body, and
        a ``Content-Type`` header is set to ``content_type``.

        The ``follow``, ``secure`` and ``extra`` arguments act the same as for
        :meth:`Client.get`.

    .. method:: Client.patch(path, data='', content_type='application/octet-stream', follow=False, secure=False, **extra)

        Makes a PATCH request on the provided ``path`` and returns a
        ``Response`` object. Useful for testing RESTful interfaces.

        The ``follow``, ``secure`` and ``extra`` arguments act the same as for
        :meth:`Client.get`.

    .. method:: Client.delete(path, data='', content_type='application/octet-stream', follow=False, secure=False, **extra)

        Makes a DELETE request on the provided ``path`` and returns a
        ``Response`` object. Useful for testing RESTful interfaces.

        When ``data`` is provided, it is used as the request body, and
        a ``Content-Type`` header is set to ``content_type``.

        The ``follow``, ``secure`` and ``extra`` arguments act the same as for
        :meth:`Client.get`.

    .. method:: Client.trace(path, follow=False, secure=False, **extra)

        Makes a TRACE request on the provided ``path`` and returns a
        ``Response`` object. Useful for simulating diagnostic probes.

        Unlike the other request methods, ``data`` is not provided as a keyword
        parameter in order to comply with :rfc:`7231#section-4.3.8`, which
        mandates that TRACE requests must not have a body.

        The ``follow``, ``secure``, and ``extra`` arguments act the same as for
        :meth:`Client.get`.

    .. method:: Client.login(**credentials)

        If your site uses Django's :doc:`authentication system</topics/auth/index>`
        and you deal with logging in users, you can use the test client's
        ``login()`` method to simulate the effect of a user logging into the
        site.

        After you call this method, the test client will have all the cookies
        and session data required to pass any login-based tests that may form
        part of a view.

        The format of the ``credentials`` argument depends on which
        :ref:`authentication backend <authentication-backends>` you're using
        (which is configured by your :setting:`AUTHENTICATION_BACKENDS`
        setting). If you're using the standard authentication backend provided
        by Django (``ModelBackend``), ``credentials`` should be the user's
        username and password, provided as keyword arguments::

            >>> c = Client()
            >>> c.login(username='fred', password='secret')

            # Now you can access a view that's only available to logged-in users.

        If you're using a different authentication backend, this method may
        require different credentials. It requires whichever credentials are
        required by your backend's ``authenticate()`` method.

        ``login()`` returns ``True`` if it the credentials were accepted and
        login was successful.

        Finally, you'll need to remember to create user accounts before you can
        use this method. As we explained above, the test runner is executed
        using a test database, which contains no users by default. As a result,
        user accounts that are valid on your production site will not work
        under test conditions. You'll need to create users as part of the test
        suite -- either manually (using the Django model API) or with a test
        fixture. Remember that if you want your test user to have a password,
        you can't set the user's password by setting the password attribute
        directly -- you must use the
        :meth:`~django.contrib.auth.models.User.set_password()` function to
        store a correctly hashed password. Alternatively, you can use the
        :meth:`~django.contrib.auth.models.UserManager.create_user` helper
        method to create a new user with a correctly hashed password.

    .. method:: Client.force_login(user, backend=None)

        If your site uses Django's :doc:`authentication
        system</topics/auth/index>`, you can use the ``force_login()`` method
        to simulate the effect of a user logging into the site. Use this method
        instead of :meth:`login` when a test requires a user be logged in and
        the details of how a user logged in aren't important.

        Unlike ``login()``, this method skips the authentication and
        verification steps: inactive users (:attr:`is_active=False
        <django.contrib.auth.models.User.is_active>`) are permitted to login
        and the user's credentials don't need to be provided.

        The user will have its ``backend`` attribute set to the value of the
        ``backend`` argument (which should be a dotted Python path string), or
        to ``settings.AUTHENTICATION_BACKENDS[0]`` if a value isn't provided.
        The :func:`~django.contrib.auth.authenticate` function called by
        :meth:`login` normally annotates the user like this.

        This method is faster than ``login()`` since the expensive
        password hashing algorithms are bypassed. Also, you can speed up
        ``login()`` by :ref:`using a weaker hasher while testing
        <speeding-up-tests-auth-hashers>`.

    .. method:: Client.logout()

        If your site uses Django's :doc:`authentication system</topics/auth/index>`,
        the ``logout()`` method can be used to simulate the effect of a user
        logging out of your site.

        After you call this method, the test client will have all the cookies
        and session data cleared to defaults. Subsequent requests will appear
        to come from an :class:`~django.contrib.auth.models.AnonymousUser`.

Testing responses
-----------------

The ``get()`` and ``post()`` methods both return a ``Response`` object. This
``Response`` object is *not* the same as the ``HttpResponse`` object returned
by Django views; the test response object has some additional data useful for
test code to verify.

Specifically, a ``Response`` object has the following attributes:

.. class:: Response()

    .. attribute:: client

        The test client that was used to make the request that resulted in the
        response.

    .. attribute:: content

        The body of the response, as a bytestring. This is the final page
        content as rendered by the view, or any error message.

    .. attribute:: context

        The template ``Context`` instance that was used to render the template that
        produced the response content.

        If the rendered page used multiple templates, then ``context`` will be a
        list of ``Context`` objects, in the order in which they were rendered.

        Regardless of the number of templates used during rendering, you can
        retrieve context values using the ``[]`` operator. For example, the
        context variable ``name`` could be retrieved using::

            >>> response = client.get('/foo/')
            >>> response.context['name']
            'Arthur'

        .. admonition:: Not using Django templates?

            This attribute is only populated when using the
            :class:`~django.template.backends.django.DjangoTemplates` backend.
            If you're using another template engine,
            :attr:`~django.template.response.SimpleTemplateResponse.context_data`
            may be a suitable alternative on responses with that attribute.

    .. attribute:: exc_info

        A tuple of three values that provides information about the unhandled
        exception, if any, that occurred during the view.

        The values are (type, value, traceback), the same as returned by
        Python's :func:`sys.exc_info`. Their meanings are:

        - *type*: The type of the exception.
        - *value*: The exception instance.
        - *traceback*: A traceback object which encapsulates the call stack at
          the point where the exception originally occurred.

        If no exception occurred, then ``exc_info`` will be ``None``.

    .. method:: json(**kwargs)

        The body of the response, parsed as JSON. Extra keyword arguments are
        passed to :func:`json.loads`. For example::

            >>> response = client.get('/foo/')
            >>> response.json()['name']
            'Arthur'

        If the ``Content-Type`` header is not ``"application/json"``, then a
        :exc:`ValueError` will be raised when trying to parse the response.

    .. attribute:: request

        The request data that stimulated the response.

    .. attribute:: wsgi_request

        The ``WSGIRequest`` instance generated by the test handler that
        generated the response.

    .. attribute:: status_code

        The HTTP status of the response, as an integer. For a full list
        of defined codes, see the `IANA status code registry`_.

        .. _IANA status code registry: https://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml

    .. attribute:: templates

        A list of ``Template`` instances used to render the final content, in
        the order they were rendered. For each template in the list, use
        ``template.name`` to get the template's file name, if the template was
        loaded from a file. (The name is a string such as
        ``'admin/index.html'``.)

        .. admonition:: Not using Django templates?

            This attribute is only populated when using the
            :class:`~django.template.backends.django.DjangoTemplates` backend.
            If you're using another template engine,
            :attr:`~django.template.response.SimpleTemplateResponse.template_name`
            may be a suitable alternative if you only need the name of the
            template used for rendering.

    .. attribute:: resolver_match

        An instance of :class:`~django.urls.ResolverMatch` for the response.
        You can use the :attr:`~django.urls.ResolverMatch.func` attribute, for
        example, to verify the view that served the response::

            # my_view here is a function based view
            self.assertEqual(response.resolver_match.func, my_view)

            # class-based views need to be compared by name, as the functions
            # generated by as_view() won't be equal
            self.assertEqual(response.resolver_match.func.__name__, MyView.as_view().__name__)

        If the given URL is not found, accessing this attribute will raise a
        :exc:`~django.urls.Resolver404` exception.

As with a normal response, you can also access the headers through
:attr:`.HttpResponse.headers`. For example, you could determine the content
type of a response using ``response.headers['Content-Type']``.

Exceptions
----------

If you point the test client at a view that raises an exception and
``Client.raise_request_exception`` is ``True``, that exception will be visible
in the test case. You can then use a standard ``try ... except`` block or
:meth:`~unittest.TestCase.assertRaises` to test for exceptions.

The only exceptions that are not visible to the test client are
:class:`~django.http.Http404`,
:class:`~django.core.exceptions.PermissionDenied`, :exc:`SystemExit`, and
:class:`~django.core.exceptions.SuspiciousOperation`. Django catches these
exceptions internally and converts them into the appropriate HTTP response
codes. In these cases, you can check ``response.status_code`` in your test.

If ``Client.raise_request_exception`` is ``False``, the test client will return a
500 response as would be returned to a browser. The response has the attribute
:attr:`~Response.exc_info` to provide information about the unhandled
exception.

Persistent state
----------------

The test client is stateful. If a response returns a cookie, then that cookie
will be stored in the test client and sent with all subsequent ``get()`` and
``post()`` requests.

Expiration policies for these cookies are not followed. If you want a cookie
to expire, either delete it manually or create a new ``Client`` instance (which
will effectively delete all cookies).

A test client has two attributes that store persistent state information. You
can access these properties as part of a test condition.

.. attribute:: Client.cookies

    A Python :class:`~http.cookies.SimpleCookie` object, containing the current
    values of all the client cookies. See the documentation of the
    :mod:`http.cookies` module for more.

.. attribute:: Client.session

    A dictionary-like object containing session information. See the
    :doc:`session documentation</topics/http/sessions>` for full details.

    To modify the session and then save it, it must be stored in a variable
    first (because a new ``SessionStore`` is created every time this property
    is accessed)::

        def test_something(self):
            session = self.client.session
            session['somekey'] = 'test'
            session.save()

Setting the language
--------------------

When testing applications that support internationalization and localization,
you might want to set the language for a test client request. The method for
doing so depends on whether or not the
:class:`~django.middleware.locale.LocaleMiddleware` is enabled.

If the middleware is enabled, the language can be set by creating a cookie with
a name of :setting:`LANGUAGE_COOKIE_NAME` and a value of the language code::

    from django.conf import settings

    def test_language_using_cookie(self):
        self.client.cookies.load({settings.LANGUAGE_COOKIE_NAME: 'fr'})
        response = self.client.get('/')
        self.assertEqual(response.content, b"Bienvenue sur mon site.")

or by including the ``Accept-Language`` HTTP header in the request::

    def test_language_using_header(self):
        response = self.client.get('/', HTTP_ACCEPT_LANGUAGE='fr')
        self.assertEqual(response.content, b"Bienvenue sur mon site.")

More details are in :ref:`how-django-discovers-language-preference`.

If the middleware isn't enabled, the active language may be set using
:func:`.translation.override`::

    from django.utils import translation

    def test_language_using_override(self):
        with translation.override('fr'):
            response = self.client.get('/')
        self.assertEqual(response.content, b"Bienvenue sur mon site.")

More details are in :ref:`explicitly-setting-the-active-language`.

Example
-------

The following is a unit test using the test client::

    import unittest
    from django.test import Client

    class SimpleTest(unittest.TestCase):
        def setUp(self):
            # Every test needs a client.
            self.client = Client()

        def test_details(self):
            # Issue a GET request.
            response = self.client.get('/customer/details/')

            # Check that the response is 200 OK.
            self.assertEqual(response.status_code, 200)

            # Check that the rendered context contains 5 customers.
            self.assertEqual(len(response.context['customers']), 5)

.. seealso::

    :class:`django.test.RequestFactory`

.. _django-testcase-subclasses:

Provided test case classes
==========================

Normal Python unit test classes extend a base class of
:class:`unittest.TestCase`. Django provides a few extensions of this base class:

.. _testcase_hierarchy_diagram:

.. figure:: _images/django_unittest_classes_hierarchy.*
   :alt: Hierarchy of Django unit testing classes (TestCase subclasses)
   :width: 508
   :height: 328

   Hierarchy of Django unit testing classes

You can convert a normal :class:`unittest.TestCase` to any of the subclasses:
change the base class of your test from ``unittest.TestCase`` to the subclass.
All of the standard Python unit test functionality will be available, and it
will be augmented with some useful additions as described in each section
below.

``SimpleTestCase``
------------------

.. class:: SimpleTestCase()

A subclass of :class:`unittest.TestCase` that adds this functionality:

* Some useful assertions like:

  * Checking that a callable :meth:`raises a certain exception
    <SimpleTestCase.assertRaisesMessage>`.
  * Checking that a callable :meth:`triggers a certain warning
    <SimpleTestCase.assertWarnsMessage>`.
  * Testing form field :meth:`rendering and error treatment
    <SimpleTestCase.assertFieldOutput>`.
  * Testing :meth:`HTML responses for the presence/lack of a given fragment
    <SimpleTestCase.assertContains>`.
  * Verifying that a template :meth:`has/hasn't been used to generate a given
    response content <SimpleTestCase.assertTemplateUsed>`.
  * Verifying that two :meth:`URLs <SimpleTestCase.assertURLEqual>` are equal.
  * Verifying a HTTP :meth:`redirect <SimpleTestCase.assertRedirects>` is
    performed by the app.
  * Robustly testing two :meth:`HTML fragments <SimpleTestCase.assertHTMLEqual>`
    for equality/inequality or :meth:`containment <SimpleTestCase.assertInHTML>`.
  * Robustly testing two :meth:`XML fragments <SimpleTestCase.assertXMLEqual>`
    for equality/inequality.
  * Robustly testing two :meth:`JSON fragments <SimpleTestCase.assertJSONEqual>`
    for equality.

* The ability to run tests with :ref:`modified settings <overriding-settings>`.
* Using the :attr:`~SimpleTestCase.client` :class:`~django.test.Client`.

If your tests make any database queries, use subclasses
:class:`~django.test.TransactionTestCase` or :class:`~django.test.TestCase`.

.. attribute:: SimpleTestCase.databases

    :class:`~SimpleTestCase` disallows database queries by default. This
    helps to avoid executing write queries which will affect other tests
    since each ``SimpleTestCase`` test isn't run in a transaction. If you
    aren't concerned about this problem, you can disable this behavior by
    setting the ``databases`` class attribute to ``'__all__'`` on your test
    class.

.. warning::

    ``SimpleTestCase`` and its subclasses (e.g. ``TestCase``, ...) rely on
    ``setUpClass()`` and ``tearDownClass()`` to perform some class-wide
    initialization (e.g. overriding settings). If you need to override those
    methods, don't forget to call the ``super`` implementation::

        class MyTestCase(TestCase):

            @classmethod
            def setUpClass(cls):
                super().setUpClass()
                ...

            @classmethod
            def tearDownClass(cls):
                ...
                super().tearDownClass()

    Be sure to account for Python's behavior if an exception is raised during
    ``setUpClass()``. If that happens, neither the tests in the class nor
    ``tearDownClass()`` are run. In the case of :class:`django.test.TestCase`,
    this will leak the transaction created in ``super()``  which results in
    various symptoms including a segmentation fault on some platforms (reported
    on macOS). If you want to intentionally raise an exception such as
    :exc:`unittest.SkipTest` in ``setUpClass()``, be sure to do it before
    calling ``super()`` to avoid this.

.. versionchanged:: 3.1

    The ``debug()`` method was implemented to allow running a test without
    collecting the result and catching exceptions.

``TransactionTestCase``
-----------------------

.. class:: TransactionTestCase()

``TransactionTestCase`` inherits from :class:`~django.test.SimpleTestCase` to
add some database-specific features:

* Resetting the database to a known state at the beginning of each test to
  ease testing and using the ORM.
* Database :attr:`~TransactionTestCase.fixtures`.
* Test :ref:`skipping based on database backend features <skipping-tests>`.
* The remaining specialized :meth:`assert*
  <TransactionTestCase.assertQuerysetEqual>` methods.

Django's :class:`TestCase` class is a more commonly used subclass of
``TransactionTestCase`` that makes use of database transaction facilities
to speed up the process of resetting the database to a known state at the
beginning of each test. A consequence of this, however, is that some database
behaviors cannot be tested within a Django ``TestCase`` class. For instance,
you cannot test that a block of code is executing within a transaction, as is
required when using
:meth:`~django.db.models.query.QuerySet.select_for_update()`. In those cases,
you should use ``TransactionTestCase``.

``TransactionTestCase`` and ``TestCase`` are identical except for the manner
in which the database is reset to a known state and the ability for test code
to test the effects of commit and rollback:

* A ``TransactionTestCase`` resets the database after the test runs by
  truncating all tables. A ``TransactionTestCase`` may call commit and rollback
  and observe the effects of these calls on the database.

* A ``TestCase``, on the other hand, does not truncate tables after a test.
  Instead, it encloses the test code in a database transaction that is rolled
  back at the end of the test. This guarantees that the rollback at the end of
  the test restores the database to its initial state.

.. warning::

  ``TestCase`` running on a database that does not support rollback (e.g. MySQL
  with the MyISAM storage engine), and all instances of ``TransactionTestCase``,
  will roll back at the end of the test by deleting all data from the test
  database.

  Apps :ref:`will not see their data reloaded <test-case-serialized-rollback>`;
  if you need this functionality (for example, third-party apps should enable
  this) you can set ``serialized_rollback = True`` inside the
  ``TestCase`` body.

``TestCase``
------------

.. class:: TestCase()

This is the most common class to use for writing tests in Django. It inherits
from :class:`TransactionTestCase` (and by extension :class:`SimpleTestCase`).
If your Django application doesn't use a database, use :class:`SimpleTestCase`.

The class:

* Wraps the tests within two nested :func:`~django.db.transaction.atomic`
  blocks: one for the whole class and one for each test. Therefore, if you want
  to test some specific database transaction behavior, use
  :class:`TransactionTestCase`.

* Checks deferrable database constraints at the end of each test.

It also provides an additional method:

.. classmethod:: TestCase.setUpTestData()

    The class-level ``atomic`` block described above allows the creation of
    initial data at the class level, once for the whole ``TestCase``. This
    technique allows for faster tests as compared to using ``setUp()``.

    For example::

        from django.test import TestCase

        class MyTests(TestCase):
            @classmethod
            def setUpTestData(cls):
                # Set up data for the whole TestCase
                cls.foo = Foo.objects.create(bar="Test")
                ...

            def test1(self):
                # Some test using self.foo
                ...

            def test2(self):
                # Some other test using self.foo
                ...

    Note that if the tests are run on a database with no transaction support
    (for instance, MySQL with the MyISAM engine), ``setUpTestData()`` will be
    called before each test, negating the speed benefits.

    .. versionchanged:: 3.2

        Objects assigned to class attributes in ``setUpTestData()`` must
        support creating deep copies with :py:func:`copy.deepcopy` in order to
        isolate them from alterations performed by each test methods. In
        previous versions of Django these objects were reused and changes made
        to them were persisted between test methods.

.. classmethod:: TestCase.captureOnCommitCallbacks(using=DEFAULT_DB_ALIAS, execute=False)

    .. versionadded:: 3.2

    Returns a context manager that captures :func:`transaction.on_commit()
    <django.db.transaction.on_commit>` callbacks for the given database
    connection. It returns a list that contains, on exit of the context, the
    captured callback functions. From this list you can make assertions on the
    callbacks or call them to invoke their side effects, emulating a commit.

    ``using`` is the alias of the database connection to capture callbacks for.

    If ``execute`` is ``True``, all the callbacks will be called as the context
    manager exits, if no exception occurred. This emulates a commit after the
    wrapped block of code.

    For example::

        from django.core import mail
        from django.test import TestCase


        class ContactTests(TestCase):
            def test_post(self):
                with self.captureOnCommitCallbacks(execute=True) as callbacks:
                    response = self.client.post(
                        '/contact/',
                        {'message': 'I like your site'},
                    )

                self.assertEqual(response.status_code, 200)
                self.assertEqual(len(callbacks), 1)
                self.assertEqual(len(mail.outbox), 1)
                self.assertEqual(mail.outbox[0].subject, 'Contact Form')
                self.assertEqual(mail.outbox[0].body, 'I like your site')

.. _live-test-server:

``LiveServerTestCase``
----------------------

.. class:: LiveServerTestCase()

``LiveServerTestCase`` does basically the same as
:class:`~django.test.TransactionTestCase` with one extra feature: it launches a
live Django server in the background on setup, and shuts it down on teardown.
This allows the use of automated test clients other than the
:ref:`Django dummy client <test-client>` such as, for example, the Selenium_
client, to execute a series of functional tests inside a browser and simulate a
real user's actions.

The live server listens on ``localhost`` and binds to port 0 which uses a free
port assigned by the operating system. The server's URL can be accessed with
``self.live_server_url`` during the tests.

To demonstrate how to use ``LiveServerTestCase``, let's write a Selenium test.
First of all, you need to install the `selenium package`_ into your Python
path:

.. console::

    $ python -m pip install selenium

Then, add a ``LiveServerTestCase``-based test to your app's tests module
(for example: ``myapp/tests.py``). For this example, we'll assume you're using
the :mod:`~django.contrib.staticfiles` app and want to have static files served
during the execution of your tests similar to what we get at development time
with ``DEBUG=True``, i.e. without having to collect them using
:djadmin:`collectstatic`. We'll use
the  :class:`~django.contrib.staticfiles.testing.StaticLiveServerTestCase`
subclass which provides that functionality. Replace it with
``django.test.LiveServerTestCase`` if you don't need that.

The code for this test may look as follows::

    from django.contrib.staticfiles.testing import StaticLiveServerTestCase
    from selenium.webdriver.firefox.webdriver import WebDriver

    class MySeleniumTests(StaticLiveServerTestCase):
        fixtures = ['user-data.json']

        @classmethod
        def setUpClass(cls):
            super().setUpClass()
            cls.selenium = WebDriver()
            cls.selenium.implicitly_wait(10)

        @classmethod
        def tearDownClass(cls):
            cls.selenium.quit()
            super().tearDownClass()

        def test_login(self):
            self.selenium.get('%s%s' % (self.live_server_url, '/login/'))
            username_input = self.selenium.find_element_by_name("username")
            username_input.send_keys('myuser')
            password_input = self.selenium.find_element_by_name("password")
            password_input.send_keys('secret')
            self.selenium.find_element_by_xpath('//input[@value="Log in"]').click()

Finally, you may run the test as follows:

.. console::

    $ ./manage.py test myapp.tests.MySeleniumTests.test_login

This example will automatically open Firefox then go to the login page, enter
the credentials and press the "Log in" button. Selenium offers other drivers in
case you do not have Firefox installed or wish to use another browser. The
example above is just a tiny fraction of what the Selenium client can do; check
out the `full reference`_ for more details.

.. _Selenium: https://www.selenium.dev/
.. _selenium package: https://pypi.org/project/selenium/
.. _full reference: https://selenium-python.readthedocs.io/api.html
.. _Firefox: https://www.mozilla.com/firefox/

.. note::

    When using an in-memory SQLite database to run the tests, the same database
    connection will be shared by two threads in parallel: the thread in which
    the live server is run and the thread in which the test case is run. It's
    important to prevent simultaneous database queries via this shared
    connection by the two threads, as that may sometimes randomly cause the
    tests to fail. So you need to ensure that the two threads don't access the
    database at the same time. In particular, this means that in some cases
    (for example, just after clicking a link or submitting a form), you might
    need to check that a response is received by Selenium and that the next
    page is loaded before proceeding with further test execution.
    Do this, for example, by making Selenium wait until the ``<body>`` HTML tag
    is found in the response (requires Selenium > 2.13)::

        def test_login(self):
            from selenium.webdriver.support.wait import WebDriverWait
            timeout = 2
            ...
            self.selenium.find_element_by_xpath('//input[@value="Log in"]').click()
            # Wait until the response is received
            WebDriverWait(self.selenium, timeout).until(
                lambda driver: driver.find_element_by_tag_name('body'))

    The tricky thing here is that there's really no such thing as a "page load,"
    especially in modern Web apps that generate HTML dynamically after the
    server generates the initial document. So, checking for the presence of
    ``<body>`` in the response might not necessarily be appropriate for all use
    cases. Please refer to the `Selenium FAQ`_ and `Selenium documentation`_
    for more information.

    .. _Selenium FAQ: https://web.archive.org/web/20160129132110/http://code.google.com/p/selenium/wiki/FrequentlyAskedQuestions#Q:_WebDriver_fails_to_find_elements_/_Does_not_block_on_page_loa
    .. _Selenium documentation: https://www.selenium.dev/documentation/webdriver/waits/#explicit-wait

Test cases features
===================

Default test client
-------------------

.. attribute:: SimpleTestCase.client

Every test case in a ``django.test.*TestCase`` instance has access to an
instance of a Django test client. This client can be accessed as
``self.client``. This client is recreated for each test, so you don't have to
worry about state (such as cookies) carrying over from one test to another.

This means, instead of instantiating a ``Client`` in each test::

    import unittest
    from django.test import Client

    class SimpleTest(unittest.TestCase):
        def test_details(self):
            client = Client()
            response = client.get('/customer/details/')
            self.assertEqual(response.status_code, 200)

        def test_index(self):
            client = Client()
            response = client.get('/customer/index/')
            self.assertEqual(response.status_code, 200)

...you can refer to ``self.client``, like so::

    from django.test import TestCase

    class SimpleTest(TestCase):
        def test_details(self):
            response = self.client.get('/customer/details/')
            self.assertEqual(response.status_code, 200)

        def test_index(self):
            response = self.client.get('/customer/index/')
            self.assertEqual(response.status_code, 200)

Customizing the test client
---------------------------

.. attribute:: SimpleTestCase.client_class

If you want to use a different ``Client`` class (for example, a subclass
with customized behavior), use the :attr:`~SimpleTestCase.client_class` class
attribute::

    from django.test import Client, TestCase

    class MyTestClient(Client):
        # Specialized methods for your environment
        ...

    class MyTest(TestCase):
        client_class = MyTestClient

        def test_my_stuff(self):
            # Here self.client is an instance of MyTestClient...
            call_some_test_code()

.. _topics-testing-fixtures:

Fixture loading
---------------

.. attribute:: TransactionTestCase.fixtures

A test case for a database-backed website isn't much use if there isn't any
data in the database. Tests are more readable and it's more maintainable to
create objects using the ORM, for example in :meth:`TestCase.setUpTestData`,
however, you can also use fixtures.

A fixture is a collection of data that Django knows how to import into a
database. For example, if your site has user accounts, you might set up a
fixture of fake user accounts in order to populate your database during tests.

The most straightforward way of creating a fixture is to use the
:djadmin:`manage.py dumpdata <dumpdata>` command. This assumes you
already have some data in your database. See the :djadmin:`dumpdata
documentation<dumpdata>` for more details.

Once you've created a fixture and placed it in a ``fixtures`` directory in one
of your :setting:`INSTALLED_APPS`, you can use it in your unit tests by
specifying a ``fixtures`` class attribute on your :class:`django.test.TestCase`
subclass::

    from django.test import TestCase
    from myapp.models import Animal

    class AnimalTestCase(TestCase):
        fixtures = ['mammals.json', 'birds']

        def setUp(self):
            # Test definitions as before.
            call_setup_methods()

        def test_fluffy_animals(self):
            # A test that uses the fixtures.
            call_some_test_code()

Here's specifically what will happen:

* At the start of each test, before ``setUp()`` is run, Django will flush the
  database, returning the database to the state it was in directly after
  :djadmin:`migrate` was called.

* Then, all the named fixtures are installed. In this example, Django will
  install any JSON fixture named ``mammals``, followed by any fixture named
  ``birds``. See the :djadmin:`loaddata` documentation for more
  details on defining and installing fixtures.

For performance reasons, :class:`TestCase` loads fixtures once for the entire
test class, before :meth:`~TestCase.setUpTestData`, instead of before each
test, and it uses transactions to clean the database before each test. In any case,
you can be certain that the outcome of a test will not be affected by another
test or by the order of test execution.

By default, fixtures are only loaded into the ``default`` database. If you are
using multiple databases and set :attr:`TransactionTestCase.databases`,
fixtures will be loaded into all specified databases.

URLconf configuration
---------------------

If your application provides views, you may want to include tests that use the
test client to exercise those views. However, an end user is free to deploy the
views in your application at any URL of their choosing. This means that your
tests can't rely upon the fact that your views will be available at a
particular URL. Decorate your test class or test method with
``@override_settings(ROOT_URLCONF=...)`` for URLconf configuration.

.. _testing-multi-db:

Multi-database support
----------------------

.. attribute:: TransactionTestCase.databases

Django sets up a test database corresponding to every database that is
defined in the :setting:`DATABASES` definition in your settings and referred to
by at least one test through ``databases``.

However, a big part of the time taken to run a Django ``TestCase`` is consumed
by the call to ``flush`` that ensures that you have a clean database at the
start of each test run. If you have multiple databases, multiple flushes are
required (one for each database), which can be a time consuming activity --
especially if your tests don't need to test multi-database activity.

As an optimization, Django only flushes the ``default`` database at
the start of each test run. If your setup contains multiple databases,
and you have a test that requires every database to be clean, you can
use the ``databases`` attribute on the test suite to request extra databases
to be flushed.

For example::

    class TestMyViews(TransactionTestCase):
        databases = {'default', 'other'}

        def test_index_page_view(self):
            call_some_test_code()

This test case will flush the ``default`` and ``other`` test databases before
running ``test_index_page_view``. You can also use ``'__all__'`` to specify
that all of the test databases must be flushed.

The ``databases`` flag also controls which databases the
:attr:`TransactionTestCase.fixtures` are loaded into. By default, fixtures are
only loaded into the ``default`` database.

Queries against databases not in ``databases`` will give assertion errors to
prevent state leaking between tests.

.. attribute:: TestCase.databases

By default, only the ``default`` database will be wrapped in a transaction
during a ``TestCase``'s execution and attempts to query other databases will
result in assertion errors to prevent state leaking between tests.

Use the ``databases`` class attribute on the test class to request transaction
wrapping against non-``default`` databases.

For example::

    class OtherDBTests(TestCase):
        databases = {'other'}

        def test_other_db_query(self):
            ...

This test will only allow queries against the ``other`` database. Just like for
:attr:`SimpleTestCase.databases` and :attr:`TransactionTestCase.databases`, the
``'__all__'`` constant can be used to specify that the test should allow
queries to all databases.

.. _overriding-settings:

Overriding settings
-------------------

.. warning::

    Use the functions below to temporarily alter the value of settings in tests.
    Don't manipulate ``django.conf.settings`` directly as Django won't restore
    the original values after such manipulations.

.. method:: SimpleTestCase.settings()

For testing purposes it's often useful to change a setting temporarily and
revert to the original value after running the testing code. For this use case
Django provides a standard Python context manager (see :pep:`343`) called
:meth:`~django.test.SimpleTestCase.settings`, which can be used like this::

    from django.test import TestCase

    class LoginTestCase(TestCase):

        def test_login(self):

            # First check for the default behavior
            response = self.client.get('/sekrit/')
            self.assertRedirects(response, '/accounts/login/?next=/sekrit/')

            # Then override the LOGIN_URL setting
            with self.settings(LOGIN_URL='/other/login/'):
                response = self.client.get('/sekrit/')
                self.assertRedirects(response, '/other/login/?next=/sekrit/')

This example will override the :setting:`LOGIN_URL` setting for the code
in the ``with`` block and reset its value to the previous state afterwards.

.. method:: SimpleTestCase.modify_settings()

It can prove unwieldy to redefine settings that contain a list of values. In
practice, adding or removing values is often sufficient. Django provides the
:meth:`~django.test.SimpleTestCase.modify_settings` context manager for easier
settings changes::

    from django.test import TestCase

    class MiddlewareTestCase(TestCase):

        def test_cache_middleware(self):
            with self.modify_settings(MIDDLEWARE={
                'append': 'django.middleware.cache.FetchFromCacheMiddleware',
                'prepend': 'django.middleware.cache.UpdateCacheMiddleware',
                'remove': [
                    'django.contrib.sessions.middleware.SessionMiddleware',
                    'django.contrib.auth.middleware.AuthenticationMiddleware',
                    'django.contrib.messages.middleware.MessageMiddleware',
                ],
            }):
                response = self.client.get('/')
                # ...

For each action, you can supply either a list of values or a string. When the
value already exists in the list, ``append`` and ``prepend`` have no effect;
neither does ``remove`` when the value doesn't exist.

.. function:: override_settings

In case you want to override a setting for a test method, Django provides the
:func:`~django.test.override_settings` decorator (see :pep:`318`). It's used
like this::

    from django.test import TestCase, override_settings

    class LoginTestCase(TestCase):

        @override_settings(LOGIN_URL='/other/login/')
        def test_login(self):
            response = self.client.get('/sekrit/')
            self.assertRedirects(response, '/other/login/?next=/sekrit/')

The decorator can also be applied to :class:`~django.test.TestCase` classes::

    from django.test import TestCase, override_settings

    @override_settings(LOGIN_URL='/other/login/')
    class LoginTestCase(TestCase):

        def test_login(self):
            response = self.client.get('/sekrit/')
            self.assertRedirects(response, '/other/login/?next=/sekrit/')

.. function:: modify_settings

Likewise, Django provides the :func:`~django.test.modify_settings`
decorator::

    from django.test import TestCase, modify_settings

    class MiddlewareTestCase(TestCase):

        @modify_settings(MIDDLEWARE={
            'append': 'django.middleware.cache.FetchFromCacheMiddleware',
            'prepend': 'django.middleware.cache.UpdateCacheMiddleware',
        })
        def test_cache_middleware(self):
            response = self.client.get('/')
            # ...

The decorator can also be applied to test case classes::

    from django.test import TestCase, modify_settings

    @modify_settings(MIDDLEWARE={
        'append': 'django.middleware.cache.FetchFromCacheMiddleware',
        'prepend': 'django.middleware.cache.UpdateCacheMiddleware',
    })
    class MiddlewareTestCase(TestCase):

        def test_cache_middleware(self):
            response = self.client.get('/')
            # ...

.. note::

    When given a class, these decorators modify the class directly and return
    it; they don't create and return a modified copy of it. So if you try to
    tweak the above examples to assign the return value to a different name
    than ``LoginTestCase`` or ``MiddlewareTestCase``, you may be surprised to
    find that the original test case classes are still equally affected by the
    decorator. For a given class, :func:`~django.test.modify_settings` is
    always applied after :func:`~django.test.override_settings`.

.. warning::

    The settings file contains some settings that are only consulted during
    initialization of Django internals. If you change them with
    ``override_settings``, the setting is changed if you access it via the
    ``django.conf.settings`` module, however, Django's internals access it
    differently. Effectively, using :func:`~django.test.override_settings` or
    :func:`~django.test.modify_settings` with these settings is probably not
    going to do what you expect it to do.

    We do not recommend altering the :setting:`DATABASES` setting. Altering
    the :setting:`CACHES` setting is possible, but a bit tricky if you are
    using internals that make using of caching, like
    :mod:`django.contrib.sessions`. For example, you will have to reinitialize
    the session backend in a test that uses cached sessions and overrides
    :setting:`CACHES`.

    Finally, avoid aliasing your settings as module-level constants as
    ``override_settings()`` won't work on such values since they are
    only evaluated the first time the module is imported.

You can also simulate the absence of a setting by deleting it after settings
have been overridden, like this::

    @override_settings()
    def test_something(self):
        del settings.LOGIN_URL
        ...

When overriding settings, make sure to handle the cases in which your app's
code uses a cache or similar feature that retains state even if the setting is
changed. Django provides the :data:`django.test.signals.setting_changed`
signal that lets you register callbacks to clean up and otherwise reset state
when settings are changed.

Django itself uses this signal to reset various data:

================================ ========================
Overridden settings              Data reset
================================ ========================
USE_TZ, TIME_ZONE                Databases timezone
TEMPLATES                        Template engines
SERIALIZATION_MODULES            Serializers cache
LOCALE_PATHS, LANGUAGE_CODE      Default translation and loaded translations
MEDIA_ROOT, DEFAULT_FILE_STORAGE Default file storage
================================ ========================

.. _emptying-test-outbox:

Emptying the test outbox
------------------------

If you use any of Django's custom ``TestCase`` classes, the test runner will
clear the contents of the test email outbox at the start of each test case.

For more detail on email services during tests, see `Email services`_ below.

.. _assertions:

Assertions
----------

As Python's normal :class:`unittest.TestCase` class implements assertion methods
such as :meth:`~unittest.TestCase.assertTrue` and
:meth:`~unittest.TestCase.assertEqual`, Django's custom :class:`TestCase` class
provides a number of custom assertion methods that are useful for testing Web
applications:

The failure messages given by most of these assertion methods can be customized
with the ``msg_prefix`` argument. This string will be prefixed to any failure
message generated by the assertion. This allows you to provide additional
details that may help you to identify the location and cause of a failure in
your test suite.

.. method:: SimpleTestCase.assertRaisesMessage(expected_exception, expected_message, callable, *args, **kwargs)
            SimpleTestCase.assertRaisesMessage(expected_exception, expected_message)

    Asserts that execution of ``callable`` raises ``expected_exception`` and
    that ``expected_message`` is found in the exception's message. Any other
    outcome is reported as a failure. It's a simpler version of
    :meth:`unittest.TestCase.assertRaisesRegex` with the difference that
    ``expected_message`` isn't treated as a regular expression.

    If only the ``expected_exception`` and ``expected_message`` parameters are
    given, returns a context manager so that the code being tested can be
    written inline rather than as a function::

        with self.assertRaisesMessage(ValueError, 'invalid literal for int()'):
            int('a')

.. method:: SimpleTestCase.assertWarnsMessage(expected_warning, expected_message, callable, *args, **kwargs)
            SimpleTestCase.assertWarnsMessage(expected_warning, expected_message)

    Analogous to :meth:`SimpleTestCase.assertRaisesMessage` but for
    :meth:`~unittest.TestCase.assertWarnsRegex` instead of
    :meth:`~unittest.TestCase.assertRaisesRegex`.

.. method:: SimpleTestCase.assertFieldOutput(fieldclass, valid, invalid, field_args=None, field_kwargs=None, empty_value='')

    Asserts that a form field behaves correctly with various inputs.

    :param fieldclass: the class of the field to be tested.
    :param valid: a dictionary mapping valid inputs to their expected cleaned
        values.
    :param invalid: a dictionary mapping invalid inputs to one or more raised
        error messages.
    :param field_args: the args passed to instantiate the field.
    :param field_kwargs: the kwargs passed to instantiate the field.
    :param empty_value: the expected clean output for inputs in ``empty_values``.

    For example, the following code tests that an ``EmailField`` accepts
    ``a@a.com`` as a valid email address, but rejects ``aaa`` with a reasonable
    error message::

        self.assertFieldOutput(EmailField, {'a@a.com': 'a@a.com'}, {'aaa': ['Enter a valid email address.']})

.. method:: SimpleTestCase.assertFormError(response, form, field, errors, msg_prefix='')

    Asserts that a field on a form raises the provided list of errors when
    rendered on the form.

    ``form`` is the name the ``Form`` instance was given in the template
    context.

    ``field`` is the name of the field on the form to check. If ``field``
    has a value of ``None``, non-field errors (errors you can access via
    :meth:`form.non_field_errors() <django.forms.Form.non_field_errors>`) will
    be checked.

    ``errors`` is an error string, or a list of error strings, that are
    expected as a result of form validation.

.. method:: SimpleTestCase.assertFormsetError(response, formset, form_index, field, errors, msg_prefix='')

    Asserts that the ``formset`` raises the provided list of errors when
    rendered.

    ``formset`` is the name the ``Formset`` instance was given in the template
    context.

    ``form_index`` is the number of the form within the ``Formset``.  If
    ``form_index`` has a value of ``None``, non-form errors (errors you can
    access via ``formset.non_form_errors()``) will be checked.

    ``field`` is the name of the field on the form to check. If ``field``
    has a value of ``None``, non-field errors (errors you can access via
    :meth:`form.non_field_errors() <django.forms.Form.non_field_errors>`) will
    be checked.

    ``errors`` is an error string, or a list of error strings, that are
    expected as a result of form validation.

.. method:: SimpleTestCase.assertContains(response, text, count=None, status_code=200, msg_prefix='', html=False)

    Asserts that a ``Response`` instance produced the given ``status_code`` and
    that ``text`` appears in the content of the response. If ``count`` is
    provided, ``text`` must occur exactly ``count`` times in the response.

    Set ``html`` to ``True`` to handle ``text`` as HTML. The comparison with
    the response content will be based on HTML semantics instead of
    character-by-character equality. Whitespace is ignored in most cases,
    attribute ordering is not significant. See
    :meth:`~SimpleTestCase.assertHTMLEqual` for more details.

.. method:: SimpleTestCase.assertNotContains(response, text, status_code=200, msg_prefix='', html=False)

    Asserts that a ``Response`` instance produced the given ``status_code`` and
    that ``text`` does *not* appear in the content of the response.

    Set ``html`` to ``True`` to handle ``text`` as HTML. The comparison with
    the response content will be based on HTML semantics instead of
    character-by-character equality. Whitespace is ignored in most cases,
    attribute ordering is not significant. See
    :meth:`~SimpleTestCase.assertHTMLEqual` for more details.

.. method:: SimpleTestCase.assertTemplateUsed(response, template_name, msg_prefix='', count=None)

    Asserts that the template with the given name was used in rendering the
    response.

    The name is a string such as ``'admin/index.html'``.

    The count argument is an integer indicating the number of times the
    template should be rendered. Default is ``None``, meaning that the template
    should be rendered one or more times.

    You can use this as a context manager, like this::

        with self.assertTemplateUsed('index.html'):
            render_to_string('index.html')
        with self.assertTemplateUsed(template_name='index.html'):
            render_to_string('index.html')

.. method:: SimpleTestCase.assertTemplateNotUsed(response, template_name, msg_prefix='')

    Asserts that the template with the given name was *not* used in rendering
    the response.

    You can use this as a context manager in the same way as
    :meth:`~SimpleTestCase.assertTemplateUsed`.

.. method:: SimpleTestCase.assertURLEqual(url1, url2, msg_prefix='')

    Asserts that two URLs are the same, ignoring the order of query string
    parameters except for parameters with the same name. For example,
    ``/path/?x=1&y=2`` is equal to ``/path/?y=2&x=1``, but
    ``/path/?a=1&a=2`` isn't equal to ``/path/?a=2&a=1``.

.. method:: SimpleTestCase.assertRedirects(response, expected_url, status_code=302, target_status_code=200, msg_prefix='', fetch_redirect_response=True)

    Asserts that the response returned a ``status_code`` redirect status,
    redirected to ``expected_url`` (including any ``GET`` data), and that the
    final page was received with ``target_status_code``.

    If your request used the ``follow`` argument, the ``expected_url`` and
    ``target_status_code`` will be the url and status code for the final
    point of the redirect chain.

    If ``fetch_redirect_response`` is ``False``, the final page won't be
    loaded. Since the test client can't fetch external URLs, this is
    particularly useful if ``expected_url`` isn't part of your Django app.

    Scheme is handled correctly when making comparisons between two URLs. If
    there isn't any scheme specified in the location where we are redirected to,
    the original request's scheme is used. If present, the scheme in
    ``expected_url`` is the one used to make the comparisons to.

.. method:: SimpleTestCase.assertHTMLEqual(html1, html2, msg=None)

    Asserts that the strings ``html1`` and ``html2`` are equal. The comparison
    is based on HTML semantics. The comparison takes following things into
    account:

    * Whitespace before and after HTML tags is ignored.
    * All types of whitespace are considered equivalent.
    * All open tags are closed implicitly, e.g. when a surrounding tag is
      closed or the HTML document ends.
    * Empty tags are equivalent to their self-closing version.
    * The ordering of attributes of an HTML element is not significant.
    * Attributes without an argument are equal to attributes that equal in
      name and value (see the examples).
    * Text, character references, and entity references that refer to the same
      character are equivalent.

    The following examples are valid tests and don't raise any
    ``AssertionError``::

        self.assertHTMLEqual(
            '<p>Hello <b>&#x27;world&#x27;!</p>',
            '''<p>
                Hello   <b>&#39;world&#39;! </b>
            </p>'''
        )
        self.assertHTMLEqual(
            '<input type="checkbox" checked="checked" id="id_accept_terms" />',
            '<input id="id_accept_terms" type="checkbox" checked>'
        )

    ``html1`` and ``html2`` must contain HTML. An ``AssertionError`` will be
    raised if one of them cannot be parsed.

    Output in case of error can be customized with the ``msg`` argument.

.. method:: SimpleTestCase.assertHTMLNotEqual(html1, html2, msg=None)

    Asserts that the strings ``html1`` and ``html2`` are *not* equal. The
    comparison is based on HTML semantics. See
    :meth:`~SimpleTestCase.assertHTMLEqual` for details.

    ``html1`` and ``html2`` must contain HTML. An ``AssertionError`` will be
    raised if one of them cannot be parsed.

    Output in case of error can be customized with the ``msg`` argument.

.. method:: SimpleTestCase.assertXMLEqual(xml1, xml2, msg=None)

    Asserts that the strings ``xml1`` and ``xml2`` are equal. The
    comparison is based on XML semantics. Similarly to
    :meth:`~SimpleTestCase.assertHTMLEqual`, the comparison is
    made on parsed content, hence only semantic differences are considered, not
    syntax differences. When invalid XML is passed in any parameter, an
    ``AssertionError`` is always raised, even if both strings are identical.

    XML declaration, document type, processing instructions, and comments are
    ignored. Only the root element and its children are compared.

    Output in case of error can be customized with the ``msg`` argument.

.. method:: SimpleTestCase.assertXMLNotEqual(xml1, xml2, msg=None)

    Asserts that the strings ``xml1`` and ``xml2`` are *not* equal. The
    comparison is based on XML semantics. See
    :meth:`~SimpleTestCase.assertXMLEqual` for details.

    Output in case of error can be customized with the ``msg`` argument.

.. method:: SimpleTestCase.assertInHTML(needle, haystack, count=None, msg_prefix='')

    Asserts that the HTML fragment ``needle`` is contained in the ``haystack`` one.

    If the ``count`` integer argument is specified, then additionally the number
    of ``needle`` occurrences will be strictly verified.

    Whitespace in most cases is ignored, and attribute ordering is not
    significant. See :meth:`~SimpleTestCase.assertHTMLEqual` for more details.

.. method:: SimpleTestCase.assertJSONEqual(raw, expected_data, msg=None)

    Asserts that the JSON fragments ``raw`` and ``expected_data`` are equal.
    Usual JSON non-significant whitespace rules apply as the heavyweight is
    delegated to the :mod:`json` library.

    Output in case of error can be customized with the ``msg`` argument.

.. method:: SimpleTestCase.assertJSONNotEqual(raw, expected_data, msg=None)

    Asserts that the JSON fragments ``raw`` and ``expected_data`` are *not* equal.
    See :meth:`~SimpleTestCase.assertJSONEqual` for further details.

    Output in case of error can be customized with the ``msg`` argument.

.. method:: TransactionTestCase.assertQuerysetEqual(qs, values, transform=None, ordered=True, msg=None)

    Asserts that a queryset ``qs`` matches a particular iterable of values
    ``values``.

    If ``transform`` is provided, ``values`` is compared to a list produced by
    applying ``transform`` to each member of ``qs``.

    By default, the comparison is also ordering dependent. If ``qs`` doesn't
    provide an implicit ordering, you can set the ``ordered`` parameter to
    ``False``, which turns the comparison into a ``collections.Counter`` comparison.
    If the order is undefined (if the given ``qs`` isn't ordered and the
    comparison is against more than one ordered value), a ``ValueError`` is
    raised.

    Output in case of error can be customized with the ``msg`` argument.

    .. versionchanged:: 3.2

        The default value of ``transform`` argument was changed to ``None``.

    .. versionadded:: 3.2

        Support for direct comparison between querysets was added.

    .. deprecated:: 3.2

        If ``transform`` is not provided and ``values`` is a list of strings,
        it's compared to a list produced by applying ``repr()`` to each member
        of ``qs``. This behavior is deprecated and will be removed in Django
        4.1. If you need it, explicitly set ``transform`` to ``repr``.

.. method:: TransactionTestCase.assertNumQueries(num, func, *args, **kwargs)

    Asserts that when ``func`` is called with ``*args`` and ``**kwargs`` that
    ``num`` database queries are executed.

    If a ``"using"`` key is present in ``kwargs`` it is used as the database
    alias for which to check the number of queries::

        self.assertNumQueries(7, using='non_default_db')

    If you wish to call a function with a ``using`` parameter you can do it by
    wrapping the call with a ``lambda`` to add an extra parameter::

        self.assertNumQueries(7, lambda: my_function(using=7))

    You can also use this as a context manager::

        with self.assertNumQueries(2):
            Person.objects.create(name="Aaron")
            Person.objects.create(name="Daniel")

.. _topics-tagging-tests:

Tagging tests
-------------

You can tag your tests so you can easily run a particular subset. For example,
you might label fast or slow tests::

    from django.test import tag

    class SampleTestCase(TestCase):

        @tag('fast')
        def test_fast(self):
            ...

        @tag('slow')
        def test_slow(self):
            ...

        @tag('slow', 'core')
        def test_slow_but_core(self):
            ...

You can also tag a test case::

    @tag('slow', 'core')
    class SampleTestCase(TestCase):
        ...

Subclasses inherit tags from superclasses, and methods inherit tags from their
class. Given::

    @tag('foo')
    class SampleTestCaseChild(SampleTestCase):

        @tag('bar')
        def test(self):
            ...

``SampleTestCaseChild.test`` will be labeled with ``'slow'``, ``'core'``,
``'bar'``, and ``'foo'``.

Then you can choose which tests to run. For example, to run only fast tests:

.. console::

    $ ./manage.py test --tag=fast

Or to run fast tests and the core one (even though it's slow):

.. console::

    $ ./manage.py test --tag=fast --tag=core

You can also exclude tests by tag. To run core tests if they are not slow:

.. console::

    $ ./manage.py test --tag=core --exclude-tag=slow

:option:`test --exclude-tag` has precedence over :option:`test --tag`, so if a
test has two tags and you select one of them and exclude the other, the test
won't be run.

.. _async-tests:

Testing asynchronous code
=========================

.. versionadded:: 3.1

If you merely want to test the output of your asynchronous views, the standard
test client will run them inside their own asynchronous loop without any extra
work needed on your part.

However, if you want to write fully-asynchronous tests for a Django project,
you will need to take several things into account.

Firstly, your tests must be ``async def`` methods on the test class (in order
to give them an asynchronous context). Django will automatically detect
any ``async def`` tests and wrap them so they run in their own event loop.

If you are testing from an asynchronous function, you must also use the
asynchronous test client. This is available as ``django.test.AsyncClient``,
or as ``self.async_client`` on any test.

``AsyncClient`` has the same methods and signatures as the synchronous (normal)
test client, with two exceptions:

* The ``follow`` parameter is not supported.
* Headers passed as ``extra`` keyword arguments should not have the ``HTTP_``
  prefix required by the synchronous client (see :meth:`Client.get`). For
  example, here is how to set an HTTP ``Accept`` header::

    >>> c = AsyncClient()
    >>> c.get(
    ...     '/customers/details/',
    ...     {'name': 'fred', 'age': 7},
    ...     ACCEPT='application/json'
    ... )

Using ``AsyncClient`` any method that makes a request must be awaited::

    async def test_my_thing(self):
        response = await self.async_client.get('/some-url/')
        self.assertEqual(response.status_code, 200)

The asynchronous client can also call synchronous views; it runs through
Django's :doc:`asynchronous request path </topics/async>`, which supports both.
Any view called through the ``AsyncClient`` will get an ``ASGIRequest`` object
for its ``request`` rather than the ``WSGIRequest`` that the normal client
creates.

.. warning::

    If you are using test decorators, they must be async-compatible to ensure
    they work correctly. Django's built-in decorators will behave correctly, but
    third-party ones may appear to not execute (they will "wrap" the wrong part
    of the execution flow and not your test).

    If you need to use these decorators, then you should decorate your test
    methods with :func:`~asgiref.sync.async_to_sync` *inside* of them instead::

        from asgiref.sync import async_to_sync
        from django.test import TestCase

        class MyTests(TestCase):

            @mock.patch(...)
            @async_to_sync
            async def test_my_thing(self):
                ...

.. _topics-testing-email:

Email services
==============

If any of your Django views send email using :doc:`Django's email
functionality </topics/email>`, you probably don't want to send email each time
you run a test using that view. For this reason, Django's test runner
automatically redirects all Django-sent email to a dummy outbox. This lets you
test every aspect of sending email -- from the number of messages sent to the
contents of each message -- without actually sending the messages.

The test runner accomplishes this by transparently replacing the normal
email backend with a testing backend.
(Don't worry -- this has no effect on any other email senders outside of
Django, such as your machine's mail server, if you're running one.)

.. currentmodule:: django.core.mail

.. data:: django.core.mail.outbox

During test running, each outgoing email is saved in
``django.core.mail.outbox``. This is a list of all
:class:`~django.core.mail.EmailMessage` instances that have been sent.  The
``outbox`` attribute is a special attribute that is created *only* when the
``locmem`` email backend is used. It doesn't normally exist as part of the
:mod:`django.core.mail` module and you can't import it directly. The code below
shows how to access this attribute correctly.

Here's an example test that examines ``django.core.mail.outbox`` for length
and contents::

    from django.core import mail
    from django.test import TestCase

    class EmailTest(TestCase):
        def test_send_email(self):
            # Send message.
            mail.send_mail(
                'Subject here', 'Here is the message.',
                'from@example.com', ['to@example.com'],
                fail_silently=False,
            )

            # Test that one message has been sent.
            self.assertEqual(len(mail.outbox), 1)

            # Verify that the subject of the first message is correct.
            self.assertEqual(mail.outbox[0].subject, 'Subject here')

As noted :ref:`previously <emptying-test-outbox>`, the test outbox is emptied
at the start of every test in a Django ``*TestCase``. To empty the outbox
manually, assign the empty list to ``mail.outbox``::

    from django.core import mail

    # Empty the test outbox
    mail.outbox = []

.. _topics-testing-management-commands:

Management Commands
===================

Management commands can be tested with the
:func:`~django.core.management.call_command` function. The output can be
redirected into a ``StringIO`` instance::

    from io import StringIO
    from django.core.management import call_command
    from django.test import TestCase

    class ClosepollTest(TestCase):
        def test_command_output(self):
            out = StringIO()
            call_command('closepoll', stdout=out)
            self.assertIn('Expected output', out.getvalue())

.. _skipping-tests:

Skipping tests
==============

.. currentmodule:: django.test

The unittest library provides the :func:`@skipIf <unittest.skipIf>` and
:func:`@skipUnless <unittest.skipUnless>` decorators to allow you to skip tests
if you know ahead of time that those tests are going to fail under certain
conditions.

For example, if your test requires a particular optional library in order to
succeed, you could decorate the test case with :func:`@skipIf
<unittest.skipIf>`. Then, the test runner will report that the test wasn't
executed and why, instead of failing the test or omitting the test altogether.

To supplement these test skipping behaviors, Django provides two
additional skip decorators. Instead of testing a generic boolean,
these decorators check the capabilities of the database, and skip the
test if the database doesn't support a specific named feature.

The decorators use a string identifier to describe database features.
This string corresponds to attributes of the database connection
features class. See
:source:`django.db.backends.base.features.BaseDatabaseFeatures class
<django/db/backends/base/features.py>` for a full list of database features
that can be used as a basis for skipping tests.

.. function:: skipIfDBFeature(*feature_name_strings)

Skip the decorated test or ``TestCase`` if all of the named database features
are supported.

For example, the following test will not be executed if the database
supports transactions (e.g., it would *not* run under PostgreSQL, but
it would under MySQL with MyISAM tables)::

    class MyTests(TestCase):
        @skipIfDBFeature('supports_transactions')
        def test_transaction_behavior(self):
            # ... conditional test code
            pass

.. function:: skipUnlessDBFeature(*feature_name_strings)

Skip the decorated test or ``TestCase`` if any of the named database features
are *not* supported.

For example, the following test will only be executed if the database
supports transactions (e.g., it would run under PostgreSQL, but *not*
under MySQL with MyISAM tables)::

    class MyTests(TestCase):
        @skipUnlessDBFeature('supports_transactions')
        def test_transaction_behavior(self):
            # ... conditional test code
            pass
