django/docs/topics/testing/advanced.txt

=======================
Advanced testing topics
=======================

The request factory
===================

.. currentmodule:: django.test

.. class:: RequestFactory

The :class:`~django.test.RequestFactory` shares the same API as
the test client. However, instead of behaving like a browser, the
RequestFactory provides a way to generate a request instance that can
be used as the first argument to any view. This means you can test a
view function the same way as you would test any other function -- as
a black box, with exactly known inputs, testing for specific outputs.

The API for the :class:`~django.test.RequestFactory` is a slightly
restricted subset of the test client API:

* It only has access to the HTTP methods :meth:`~Client.get()`,
  :meth:`~Client.post()`, :meth:`~Client.put()`,
  :meth:`~Client.delete()`, :meth:`~Client.head()`,
  :meth:`~Client.options()`, and :meth:`~Client.trace()`.

* These methods accept all the same arguments *except* for
  ``follow``. Since this is just a factory for producing
  requests, it's up to you to handle the response.

* It does not support middleware. Session and authentication
  attributes must be supplied by the test itself if required
  for the view to function properly.

Example
-------

The following is a simple unit test using the request factory::

    from django.contrib.auth.models import AnonymousUser, User
    from django.test import RequestFactory, TestCase

    from .views import MyView, my_view

    class SimpleTest(TestCase):
        def setUp(self):
            # Every test needs access to the request factory.
            self.factory = RequestFactory()
            self.user = User.objects.create_user(
                username='jacob', email='jacob@…', password='top_secret')

        def test_details(self):
            # Create an instance of a GET request.
            request = self.factory.get('/customer/details')

            # Recall that middleware are not supported. You can simulate a
            # logged-in user by setting request.user manually.
            request.user = self.user

            # Or you can simulate an anonymous user by setting request.user to
            # an AnonymousUser instance.
            request.user = AnonymousUser()

            # Test my_view() as if it were deployed at /customer/details
            response = my_view(request)
            # Use this syntax for class-based views.
            response = MyView.as_view()(request)
            self.assertEqual(response.status_code, 200)

.. _topics-testing-advanced-multiple-hosts:

Tests and multiple host names
=============================

The :setting:`ALLOWED_HOSTS` setting is validated when running tests. This
allows the test client to differentiate between internal and external URLs.

Projects that support multitenancy or otherwise alter business logic based on
the request's host and use custom host names in tests must include those hosts
in :setting:`ALLOWED_HOSTS`.

The first and simplest option to do so is to add the hosts to your settings
file. For example, the test suite for docs.djangoproject.com includes the
following::

    from django.test import TestCase

    class SearchFormTestCase(TestCase):
        def test_empty_get(self):
            response = self.client.get('/en/dev/search/', HTTP_HOST='docs.djangoproject.dev:8000')
            self.assertEqual(response.status_code, 200)

and the settings file includes a list of the domains supported by the project::

    ALLOWED_HOSTS = [
        'www.djangoproject.dev',
        'docs.djangoproject.dev',
        ...
    ]

Another option is to add the required hosts to :setting:`ALLOWED_HOSTS` using
:meth:`~django.test.override_settings()` or
:attr:`~django.test.SimpleTestCase.modify_settings()`. This option may be
preferable in standalone apps that can't package their own settings file or
for projects where the list of domains is not static (e.g., subdomains for
multitenancy). For example, you could write a test for the domain
``http://otherserver/`` as follows::

    from django.test import TestCase, override_settings

    class MultiDomainTestCase(TestCase):
        @override_settings(ALLOWED_HOSTS=['otherserver'])
        def test_other_domain(self):
            response = self.client.get('http://otherserver/foo/bar/')

Disabling :setting:`ALLOWED_HOSTS` checking (``ALLOWED_HOSTS = ['*']``) when
running tests prevents the test client from raising a helpful error message if
you follow a redirect to an external URL.

.. _topics-testing-advanced-multidb:

Tests and multiple databases
============================

.. _topics-testing-primaryreplica:

Testing primary/replica configurations
--------------------------------------

If you're testing a multiple database configuration with primary/replica
(referred to as master/slave by some databases) replication, this strategy of
creating test databases poses a problem.
When the test databases are created, there won't be any replication,
and as a result, data created on the primary won't be seen on the
replica.

To compensate for this, Django allows you to define that a database is
a *test mirror*. Consider the following (simplified) example database
configuration::

    DATABASES = {
        'default': {
            'ENGINE': 'django.db.backends.mysql',
            'NAME': 'myproject',
            'HOST': 'dbprimary',
             # ... plus some other settings
        },
        'replica': {
            'ENGINE': 'django.db.backends.mysql',
            'NAME': 'myproject',
            'HOST': 'dbreplica',
            'TEST': {
                'MIRROR': 'default',
            },
            # ... plus some other settings
        }
    }

In this setup, we have two database servers: ``dbprimary``, described
by the database alias ``default``, and ``dbreplica`` described by the
alias ``replica``. As you might expect, ``dbreplica`` has been configured
by the database administrator as a read replica of ``dbprimary``, so in
normal activity, any write to ``default`` will appear on ``replica``.

If Django created two independent test databases, this would break any
tests that expected replication to occur. However, the ``replica``
database has been configured as a test mirror (using the
:setting:`MIRROR <TEST_MIRROR>` test setting), indicating that under
testing, ``replica`` should be treated as a mirror of ``default``.

When the test environment is configured, a test version of ``replica``
will *not* be created. Instead the connection to ``replica``
will be redirected to point at ``default``. As a result, writes to
``default`` will appear on ``replica`` -- but because they are actually
the same database, not because there is data replication between the
two databases.

.. _topics-testing-creation-dependencies:

Controlling creation order for test databases
---------------------------------------------

By default, Django will assume all databases depend on the ``default``
database and therefore always create the ``default`` database first.
However, no guarantees are made on the creation order of any other
databases in your test setup.

If your database configuration requires a specific creation order, you
can specify the dependencies that exist using the :setting:`DEPENDENCIES
<TEST_DEPENDENCIES>` test setting. Consider the following (simplified)
example database configuration::

    DATABASES = {
        'default': {
            # ... db settings
            'TEST': {
                'DEPENDENCIES': ['diamonds'],
            },
        },
        'diamonds': {
            # ... db settings
            'TEST': {
                'DEPENDENCIES': [],
            },
        },
        'clubs': {
            # ... db settings
            'TEST': {
                'DEPENDENCIES': ['diamonds'],
            },
        },
        'spades': {
            # ... db settings
            'TEST': {
                'DEPENDENCIES': ['diamonds', 'hearts'],
            },
        },
        'hearts': {
            # ... db settings
            'TEST': {
                'DEPENDENCIES': ['diamonds', 'clubs'],
            },
        }
    }

Under this configuration, the ``diamonds`` database will be created first,
as it is the only database alias without dependencies. The ``default`` and
``clubs`` alias will be created next (although the order of creation of this
pair is not guaranteed), then ``hearts``, and finally ``spades``.

If there are any circular dependencies in the :setting:`DEPENDENCIES
<TEST_DEPENDENCIES>` definition, an
:exc:`~django.core.exceptions.ImproperlyConfigured` exception will be raised.

Advanced features of ``TransactionTestCase``
============================================

.. attribute:: TransactionTestCase.available_apps

    .. warning::

        This attribute is a private API. It may be changed or removed without
        a deprecation period in the future, for instance to accommodate changes
        in application loading.

        It's used to optimize Django's own test suite, which contains hundreds
        of models but no relations between models in different applications.

    By default, ``available_apps`` is set to ``None``. After each test, Django
    calls :djadmin:`flush` to reset the database state. This empties all tables
    and emits the :data:`~django.db.models.signals.post_migrate` signal, which
    re-creates one content type and three permissions for each model. This
    operation gets expensive proportionally to the number of models.

    Setting ``available_apps`` to a list of applications instructs Django to
    behave as if only the models from these applications were available. The
    behavior of ``TransactionTestCase`` changes as follows:

    - :data:`~django.db.models.signals.post_migrate` is fired before each
      test to create the content types and permissions for each model in
      available apps, in case they're missing.
    - After each test, Django empties only tables corresponding to models in
      available apps. However, at the database level, truncation may cascade to
      related models in unavailable apps. Furthermore
      :data:`~django.db.models.signals.post_migrate` isn't fired; it will be
      fired by the next ``TransactionTestCase``, after the correct set of
      applications is selected.

    Since the database isn't fully flushed, if a test creates instances of
    models not included in ``available_apps``, they will leak and they may
    cause unrelated tests to fail. Be careful with tests that use sessions;
    the default session engine stores them in the database.

    Since :data:`~django.db.models.signals.post_migrate` isn't emitted after
    flushing the database, its state after a ``TransactionTestCase`` isn't the
    same as after a ``TestCase``: it's missing the rows created by listeners
    to :data:`~django.db.models.signals.post_migrate`. Considering the
    :ref:`order in which tests are executed <order-of-tests>`, this isn't an
    issue, provided either all ``TransactionTestCase`` in a given test suite
    declare ``available_apps``, or none of them.

    ``available_apps`` is mandatory in Django's own test suite.

.. attribute:: TransactionTestCase.reset_sequences

    Setting ``reset_sequences = True`` on a ``TransactionTestCase`` will make
    sure sequences are always reset before the test run::

        class TestsThatDependsOnPrimaryKeySequences(TransactionTestCase):
            reset_sequences = True

            def test_animal_pk(self):
                lion = Animal.objects.create(name="lion", sound="roar")
                # lion.pk is guaranteed to always be 1
                self.assertEqual(lion.pk, 1)

    Unless you are explicitly testing primary keys sequence numbers, it is
    recommended that you do not hard code primary key values in tests.

    Using ``reset_sequences = True`` will slow down the test, since the primary
    key reset is a relatively expensive database operation.

.. _testing-reusable-applications:

Using the Django test runner to test reusable applications
==========================================================

If you are writing a :doc:`reusable application </intro/reusable-apps>`
you may want to use the Django test runner to run your own test suite
and thus benefit from the Django testing infrastructure.

A common practice is a *tests* directory next to the application code, with the
following structure::

    runtests.py
    polls/
        __init__.py
        models.py
        ...
    tests/
        __init__.py
        models.py
        test_settings.py
        tests.py

Let's take a look inside a couple of those files:

.. snippet::
    :filename: runtests.py

    #!/usr/bin/env python
    import os
    import sys

    import django
    from django.conf import settings
    from django.test.utils import get_runner

    if __name__ == "__main__":
        os.environ['DJANGO_SETTINGS_MODULE'] = 'tests.test_settings'
        django.setup()
        TestRunner = get_runner(settings)
        test_runner = TestRunner()
        failures = test_runner.run_tests(["tests"])
        sys.exit(bool(failures))


This is the script that you invoke to run the test suite. It sets up the
Django environment, creates the test database and runs the tests.

For the sake of clarity, this example contains only the bare minimum
necessary to use the Django test runner. You may want to add
command-line options for controlling verbosity, passing in specific test
labels to run, etc.

.. snippet::
    :filename: tests/test_settings.py

    SECRET_KEY = 'fake-key'
    INSTALLED_APPS = [
        "tests",
    ]

This file contains the :doc:`Django settings </topics/settings>`
required to run your app's tests.

Again, this is a minimal example; your tests may require additional
settings to run.

Since the *tests* package is included in :setting:`INSTALLED_APPS` when
running your tests, you can define test-only models in its ``models.py``
file.


.. _other-testing-frameworks:

Using different testing frameworks
==================================

Clearly, :mod:`unittest` is not the only Python testing framework. While Django
doesn't provide explicit support for alternative frameworks, it does provide a
way to invoke tests constructed for an alternative framework as if they were
normal Django tests.

When you run ``./manage.py test``, Django looks at the :setting:`TEST_RUNNER`
setting to determine what to do. By default, :setting:`TEST_RUNNER` points to
``'django.test.runner.DiscoverRunner'``. This class defines the default Django
testing behavior. This behavior involves:

#. Performing global pre-test setup.

#. Looking for tests in any file below the current directory whose name matches
   the pattern ``test*.py``.

#. Creating the test databases.

#. Running ``migrate`` to install models and initial data into the test
   databases.

#. Running the :doc:`system checks </topics/checks>`.

#. Running the tests that were found.

#. Destroying the test databases.

#. Performing global post-test teardown.

If you define your own test runner class and point :setting:`TEST_RUNNER` at
that class, Django will execute your test runner whenever you run
``./manage.py test``. In this way, it is possible to use any test framework
that can be executed from Python code, or to modify the Django test execution
process to satisfy whatever testing requirements you may have.

.. _topics-testing-test_runner:

Defining a test runner
----------------------

.. currentmodule:: django.test.runner

A test runner is a class defining a ``run_tests()`` method. Django ships
with a ``DiscoverRunner`` class that defines the default Django testing
behavior. This class defines the ``run_tests()`` entry point, plus a
selection of other methods that are used to by ``run_tests()`` to set up,
execute and tear down the test suite.

.. class:: DiscoverRunner(pattern='test*.py', top_level=None, verbosity=1, interactive=True, failfast=False, keepdb=False, reverse=False, debug_mode=False, debug_sql=False, **kwargs)

    ``DiscoverRunner`` will search for tests in any file matching ``pattern``.

    ``top_level`` can be used to specify the directory containing your
    top-level Python modules. Usually Django can figure this out automatically,
    so it's not necessary to specify this option. If specified, it should
    generally be the directory containing your ``manage.py`` file.

    ``verbosity`` determines the amount of notification and debug information
    that will be printed to the console; ``0`` is no output, ``1`` is normal
    output, and ``2`` is verbose output.

    If ``interactive`` is ``True``, the test suite has permission to ask the
    user for instructions when the test suite is executed. An example of this
    behavior would be asking for permission to delete an existing test
    database. If ``interactive`` is ``False``, the test suite must be able to
    run without any manual intervention.

    If ``failfast`` is ``True``, the test suite will stop running after the
    first test failure is detected.

    If ``keepdb`` is ``True``, the test suite will use the existing database,
    or create one if necessary. If ``False``, a new database will be created,
    prompting the user to remove the existing one, if present.

    If ``reverse`` is ``True``, test cases will be executed in the opposite
    order. This could be useful to debug tests that aren't properly isolated
    and have side effects. :ref:`Grouping by test class <order-of-tests>` is
    preserved when using this option.

    ``debug_mode`` specifies what the :setting:`DEBUG` setting should be
    set to prior to running tests.

    If ``debug_sql`` is ``True``, failing test cases will output SQL queries
    logged to the :ref:`django.db.backends logger <django-db-logger>` as well
    as the traceback. If ``verbosity`` is ``2``, then queries in all tests are
    output.

    Django may, from time to time, extend the capabilities of the test runner
    by adding new arguments. The ``**kwargs`` declaration allows for this
    expansion. If you subclass ``DiscoverRunner`` or write your own test
    runner, ensure it accepts ``**kwargs``.

    Your test runner may also define additional command-line options.
    Create or override an ``add_arguments(cls, parser)`` class method and add
    custom arguments by calling ``parser.add_argument()`` inside the method, so
    that the :djadmin:`test` command will be able to use those arguments.

Attributes
~~~~~~~~~~

.. attribute:: DiscoverRunner.test_suite

    The class used to build the test suite. By default it is set to
    ``unittest.TestSuite``. This can be overridden if you wish to implement
    different logic for collecting tests.

.. attribute:: DiscoverRunner.test_runner

    This is the class of the low-level test runner which is used to execute
    the individual tests and format the results. By default it is set to
    ``unittest.TextTestRunner``. Despite the unfortunate similarity in
    naming conventions, this is not the same type of class as
    ``DiscoverRunner``, which covers a broader set of responsibilities. You
    can override this attribute to modify the way tests are run and reported.

.. attribute:: DiscoverRunner.test_loader

    This is the class that loads tests, whether from TestCases or modules or
    otherwise and bundles them into test suites for the runner to execute.
    By default it is set to ``unittest.defaultTestLoader``. You can override
    this attribute if your tests are going to be loaded in unusual ways.

Methods
~~~~~~~

.. method:: DiscoverRunner.run_tests(test_labels, extra_tests=None, **kwargs)

    Run the test suite.

    ``test_labels`` allows you to specify which tests to run and supports
    several formats (see :meth:`DiscoverRunner.build_suite` for a list of
    supported formats).

    ``extra_tests`` is a list of extra ``TestCase`` instances to add to the
    suite that is executed by the test runner. These extra tests are run
    in addition to those discovered in the modules listed in ``test_labels``.

    This method should return the number of tests that failed.

.. classmethod:: DiscoverRunner.add_arguments(parser)

    Override this class method to add custom arguments accepted by the
    :djadmin:`test` management command. See
    :py:meth:`argparse.ArgumentParser.add_argument()` for details about adding
    arguments to a parser.

.. method:: DiscoverRunner.setup_test_environment(**kwargs)

    Sets up the test environment by calling
    :func:`~django.test.utils.setup_test_environment` and setting
    :setting:`DEBUG` to ``self.debug_mode`` (defaults to ``False``).

.. method:: DiscoverRunner.build_suite(test_labels, extra_tests=None, **kwargs)

    Constructs a test suite that matches the test labels provided.

    ``test_labels`` is a list of strings describing the tests to be run. A test
    label can take one of four forms:

    * ``path.to.test_module.TestCase.test_method`` -- Run a single test method
      in a test case.
    * ``path.to.test_module.TestCase`` -- Run all the test methods in a test
      case.
    * ``path.to.module`` -- Search for and run all tests in the named Python
      package or module.
    * ``path/to/directory`` -- Search for and run all tests below the named
      directory.

    If ``test_labels`` has a value of ``None``, the test runner will search for
    tests in all files below the current directory whose names match its
    ``pattern`` (see above).

    ``extra_tests`` is a list of extra ``TestCase`` instances to add to the
    suite that is executed by the test runner. These extra tests are run
    in addition to those discovered in the modules listed in ``test_labels``.

    Returns a ``TestSuite`` instance ready to be run.

.. method:: DiscoverRunner.setup_databases(**kwargs)

    Creates the test databases by calling
    :func:`~django.test.utils.setup_databases`.

.. method:: DiscoverRunner.run_checks()

    Runs the :doc:`system checks </topics/checks>`.

.. method:: DiscoverRunner.run_suite(suite, **kwargs)

    Runs the test suite.

    Returns the result produced by the running the test suite.

.. method:: DiscoverRunner.get_test_runner_kwargs()

    Returns the keyword arguments to instantiate the
    ``DiscoverRunner.test_runner`` with.

.. method:: DiscoverRunner.teardown_databases(old_config, **kwargs)

    Destroys the test databases, restoring pre-test conditions by calling
    :func:`~django.test.utils.teardown_databases`.

.. method:: DiscoverRunner.teardown_test_environment(**kwargs)

    Restores the pre-test environment.

.. method:: DiscoverRunner.suite_result(suite, result, **kwargs)

    Computes and returns a return code based on a test suite, and the result
    from that test suite.


Testing utilities
-----------------

``django.test.utils``
~~~~~~~~~~~~~~~~~~~~~

.. module:: django.test.utils
   :synopsis: Helpers to write custom test runners.

To assist in the creation of your own test runner, Django provides a number of
utility methods in the ``django.test.utils`` module.

.. function:: setup_test_environment(debug=None)

    Performs global pre-test setup, such as installing instrumentation for the
    template rendering system and setting up the dummy email outbox.

    If ``debug`` isn't ``None``, the :setting:`DEBUG` setting is updated to its
    value.

.. function:: teardown_test_environment()

    Performs global post-test teardown, such as removing instrumentation from
    the template system and restoring normal email services.

.. function:: setup_databases(verbosity, interactive, keepdb=False, debug_sql=False, parallel=0, **kwargs)

    Creates the test databases.

    Returns a data structure that provides enough detail to undo the changes
    that have been made. This data will be provided to the
    :func:`teardown_databases` function at the conclusion of testing.

.. function:: teardown_databases(old_config, parallel=0, keepdb=False)

    Destroys the test databases, restoring pre-test conditions.

    ``old_config`` is a data structure defining the changes in the database
    configuration that need to be reversed. It's the return value of the
    :meth:`setup_databases` method.

``django.db.connection.creation``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. currentmodule:: django.db.connection.creation

The creation module of the database backend also provides some utilities that
can be useful during testing.

.. function:: create_test_db(verbosity=1, autoclobber=False, serialize=True, keepdb=False)

    Creates a new test database and runs ``migrate`` against it.

    ``verbosity`` has the same behavior as in ``run_tests()``.

    ``autoclobber`` describes the behavior that will occur if a
    database with the same name as the test database is discovered:

    * If ``autoclobber`` is ``False``, the user will be asked to
      approve destroying the existing database. ``sys.exit`` is
      called if the user does not approve.

    * If autoclobber is ``True``, the database will be destroyed
      without consulting the user.

    ``serialize`` determines if Django serializes the database into an
    in-memory JSON string before running tests (used to restore the database
    state between tests if you don't have transactions). You can set this to
    ``False`` to speed up creation time if you don't have any test classes
    with :ref:`serialized_rollback=True <test-case-serialized-rollback>`.

    If you are using the default test runner, you can control this with the
    the :setting:`SERIALIZE <TEST_SERIALIZE>` entry in the :setting:`TEST
    <DATABASE-TEST>` dictionary.

    ``keepdb`` determines if the test run should use an existing
    database, or create a new one. If ``True``, the existing
    database will be used, or created if not present. If ``False``,
    a new database will be created, prompting the user to remove
    the existing one, if present.

    Returns the name of the test database that it created.

    ``create_test_db()`` has the side effect of modifying the value of
    :setting:`NAME` in :setting:`DATABASES` to match the name of the test
    database.

.. function:: destroy_test_db(old_database_name, verbosity=1, keepdb=False)

    Destroys the database whose name is the value of :setting:`NAME` in
    :setting:`DATABASES`, and sets :setting:`NAME` to the value of
    ``old_database_name``.

    The ``verbosity`` argument has the same behavior as for
    :class:`~django.test.runner.DiscoverRunner`.

    If the ``keepdb`` argument is ``True``, then the connection to the
    database will be closed, but the database will not be destroyed.

.. _topics-testing-code-coverage:

Integration with ``coverage.py``
================================

Code coverage describes how much source code has been tested. It shows which
parts of your code are being exercised by tests and which are not. It's an
important part of testing applications, so it's strongly recommended to check
the coverage of your tests.

Django can be easily integrated with `coverage.py`_, a tool for measuring code
coverage of Python programs. First, `install coverage.py`_. Next, run the
following from your project folder containing ``manage.py``::

   coverage run --source='.' manage.py test myapp

This runs your tests and collects coverage data of the executed files in your
project. You can see a report of this data by typing following command::

   coverage report

Note that some Django code was executed while running tests, but it is not
listed here because of the ``source`` flag passed to the previous command.

For more options like annotated HTML listings detailing missed lines, see the
`coverage.py`_ docs.

.. _coverage.py: https://coverage.readthedocs.io/
.. _install coverage.py: https://pypi.org/project/coverage/