django/docs/internals/contributing/writing-code/unit-tests.txt

==========
Unit tests
==========

Django comes with a test suite of its own, in the ``tests`` directory of the
code base. It's our policy to make sure all tests pass at all times.

We appreciate any and all contributions to the test suite!

The Django tests all use the testing infrastructure that ships with Django for
testing applications. See :doc:`/topics/testing/overview` for an explanation of
how to write new tests.

.. _running-unit-tests:

Running the unit tests
======================

Quickstart
----------

First, `fork Django on GitHub <https://github.com/django/django/fork>`__.

Second, create and activate a virtual environment. If you're not familiar with
how to do that, read our :doc:`contributing tutorial </intro/contributing>`.

Next, clone your fork, install some requirements, and run the tests:

.. console::

   $ git clone https://github.com/YourGitHubName/django.git django-repo
   $ cd django-repo/tests
   $ python -m pip install -e ..
   $ python -m pip install -r requirements/py3.txt
   $ ./runtests.py

Installing the requirements will likely require some operating system packages
that your computer doesn't have installed. You can usually figure out which
package to install by doing a web search for the last line or so of the error
message. Try adding your operating system to the search query if needed.

If you have trouble installing the requirements, you can skip that step. See
:ref:`running-unit-tests-dependencies` for details on installing the optional
test dependencies. If you don't have an optional dependency installed, the
tests that require it will be skipped.

Running the tests requires a Django settings module that defines the databases
to use. To help you get started, Django provides and uses a sample settings
module that uses the SQLite database. See :ref:`running-unit-tests-settings` to
learn how to use a different settings module to run the tests with a different
database.

Having problems? See :ref:`troubleshooting-unit-tests` for some common issues.

Running tests using ``tox``
---------------------------

`Tox <https://tox.wiki/>`_ is a tool for running tests in different virtual
environments. Django includes a basic ``tox.ini`` that automates some checks
that our build server performs on pull requests. To run the unit tests and
other checks (such as :ref:`import sorting <coding-style-imports>`, the
:ref:`documentation spelling checker <documentation-spelling-check>`, and
:ref:`code formatting <coding-style-python>`), install and run the ``tox``
command from any place in the Django source tree:

.. console::

    $ python -m pip install tox
    $ tox

By default, ``tox`` runs the test suite with the bundled test settings file for
SQLite, ``black``, ``blacken-docs``, ``flake8``, ``isort``, and the
documentation spelling checker. In addition to the system dependencies noted
elsewhere in this documentation, the command ``python3`` must be on your path
and linked to the appropriate version of Python. A list of default environments
can be seen as follows:

.. console::

    $ tox -l
    py3
    black
    blacken-docs
    flake8>=3.7.0
    docs
    isort>=5.1.0

Testing other Python versions and database backends
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In addition to the default environments, ``tox`` supports running unit tests
for other versions of Python and other database backends. Since Django's test
suite doesn't bundle a settings file for database backends other than SQLite,
however, you must :ref:`create and provide your own test settings
<running-unit-tests-settings>`. For example, to run the tests on Python 3.12
using PostgreSQL:

.. console::

    $ tox -e py312-postgres -- --settings=my_postgres_settings

This command sets up a Python 3.12 virtual environment, installs Django's
test suite dependencies (including those for PostgreSQL), and calls
``runtests.py`` with the supplied arguments (in this case,
``--settings=my_postgres_settings``).

The remainder of this documentation shows commands for running tests without
``tox``, however, any option passed to ``runtests.py`` can also be passed to
``tox`` by prefixing the argument list with ``--``, as above.

``Tox`` also respects the :envvar:`DJANGO_SETTINGS_MODULE` environment
variable, if set. For example, the following is equivalent to the command
above:

.. code-block:: console

    $ DJANGO_SETTINGS_MODULE=my_postgres_settings tox -e py312-postgres

Windows users should use:

.. code-block:: doscon

    ...\> set DJANGO_SETTINGS_MODULE=my_postgres_settings
    ...\> tox -e py312-postgres

Running the JavaScript tests
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django includes a set of :ref:`JavaScript unit tests <javascript-tests>` for
functions in certain contrib apps. The JavaScript tests aren't run by default
using ``tox`` because they require ``Node.js`` to be installed and aren't
necessary for the majority of patches. To run the JavaScript tests using
``tox``:

.. console::

    $ tox -e javascript

This command runs ``npm install`` to ensure test requirements are up to
date and then runs ``npm test``.

Running tests using ``django-docker-box``
-----------------------------------------

`django-docker-box`_ allows you to run the Django's test suite across all
supported databases and python versions. See the `django-docker-box`_ project
page for installation and usage instructions.

.. _django-docker-box: https://github.com/django/django-docker-box/

.. _running-unit-tests-settings:

Using another ``settings`` module
---------------------------------

The included settings module (``tests/test_sqlite.py``) allows you to run the
test suite using SQLite. If you want to run the tests using a different
database, you'll need to define your own settings file. Some tests, such as
those for ``contrib.postgres``, are specific to a particular database backend
and will be skipped if run with a different backend. Some tests are skipped or
expected failures on a particular database backend (see
``DatabaseFeatures.django_test_skips`` and
``DatabaseFeatures.django_test_expected_failures`` on each backend).

To run the tests with different settings, ensure that the module is on your
:envvar:`PYTHONPATH` and pass the module with ``--settings``.

The :setting:`DATABASES` setting in any test settings module needs to define
two databases:

* A ``default`` database. This database should use the backend that
  you want to use for primary testing.

* A database with the alias ``other``. The ``other`` database is used to test
  that queries can be directed to different databases. This database should use
  the same backend as the ``default``, and it must have a different name.

If you're using a backend that isn't SQLite, you will need to provide other
details for each database:

* The :setting:`USER` option needs to specify an existing user account
  for the database. That user needs permission to execute ``CREATE DATABASE``
  so that the test database can be created.

* The :setting:`PASSWORD` option needs to provide the password for
  the :setting:`USER` that has been specified.

Test databases get their names by prepending ``test_`` to the value of the
:setting:`NAME` settings for the databases defined in :setting:`DATABASES`.
These test databases are deleted when the tests are finished.

You will also need to ensure that your database uses UTF-8 as the default
character set. If your database server doesn't use UTF-8 as a default charset,
you will need to include a value for :setting:`CHARSET <TEST_CHARSET>` in the
test settings dictionary for the applicable database.

.. _runtests-specifying-labels:

Running only some of the tests
------------------------------

Django's entire test suite takes a while to run, and running every single test
could be redundant if, say, you just added a test to Django that you want to
run quickly without running everything else. You can run a subset of the unit
tests by appending the names of the test modules to ``runtests.py`` on the
command line.

For example, if you'd like to run tests only for generic relations and
internationalization, type:

.. console::

   $ ./runtests.py --settings=path.to.settings generic_relations i18n

How do you find out the names of individual tests? Look in ``tests/`` — each
directory name there is the name of a test.

If you want to run only a particular class of tests, you can specify a list of
paths to individual test classes. For example, to run the ``TranslationTests``
of the ``i18n`` module, type:

.. console::

   $ ./runtests.py --settings=path.to.settings i18n.tests.TranslationTests

Going beyond that, you can specify an individual test method like this:

.. console::

   $ ./runtests.py --settings=path.to.settings i18n.tests.TranslationTests.test_lazy_objects

You can run tests starting at a specified top-level module with ``--start-at``
option. For example:

.. console::

   $ ./runtests.py --start-at=wsgi

You can also run tests starting after a specified top-level module with
``--start-after`` option. For example:

.. console::

   $ ./runtests.py --start-after=wsgi

Note that the ``--reverse`` option doesn't impact on ``--start-at`` or
``--start-after`` options. Moreover these options cannot be used with test
labels.

.. _running-selenium-tests:

Running the Selenium tests
--------------------------

Some tests require Selenium and a web browser. To run these tests, you must
install the :pypi:`selenium` package and run the tests with the
``--selenium=<BROWSERS>`` option. For example, if you have Firefox and Google
Chrome installed:

.. console::

   $ ./runtests.py --selenium=firefox,chrome

See the `selenium.webdriver`_ package for the list of available browsers.

Specifying ``--selenium`` automatically sets ``--tags=selenium`` to run only
the tests that require selenium.

Some browsers (e.g. Chrome or Firefox) support headless testing, which can be
faster and more stable. Add the ``--headless`` option to enable this mode.

.. _selenium.webdriver: https://github.com/SeleniumHQ/selenium/tree/trunk/py/selenium/webdriver

For testing changes to the admin UI, the selenium tests can be run with the
``--screenshots`` option enabled. Screenshots will be saved to the
``tests/screenshots/`` directory.

To define when screenshots should be taken during a selenium test, the test
class must use the ``@django.test.selenium.screenshot_cases`` decorator with a
list of supported screenshot types (``"desktop_size"``, ``"mobile_size"``,
``"small_screen_size"``, ``"rtl"``, ``"dark"``, and ``"high_contrast"``). It
can then call ``self.take_screenshot("unique-screenshot-name")`` at the desired
point to generate the screenshots. For example::

    from django.test.selenium import SeleniumTestCase, screenshot_cases
    from django.urls import reverse


    class SeleniumTests(SeleniumTestCase):
        @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark", "high_contrast"])
        def test_login_button_centered(self):
            self.selenium.get(self.live_server_url + reverse("admin:login"))
            self.take_screenshot("login")
            ...

This generates multiple screenshots of the login page - one for a desktop
screen, one for a mobile screen, one for right-to-left languages on desktop,
one for the dark mode on desktop, and one for high contrast mode on desktop
when using chrome.

.. _running-unit-tests-dependencies:

Running all the tests
---------------------

If you want to run the full suite of tests, you'll need to install a number of
dependencies:

* :pypi:`aiosmtpd` 1.4.5+
* :pypi:`argon2-cffi` 23.1.0+
* :pypi:`asgiref` 3.8.1+ (required)
* :pypi:`bcrypt` 4.1.1+
* :pypi:`colorama` 0.4.6+
* :pypi:`docutils` 0.19+
* :pypi:`geoip2` 4.8.0+
* :pypi:`Jinja2` 2.11+
* :pypi:`numpy` 1.26.0+
* :pypi:`Pillow` 10.1.0+
* :pypi:`PyYAML` 6.0.2+
* :pypi:`pywatchman`
* :pypi:`redis` 5.1.0+
* :pypi:`setuptools`
* :pypi:`pymemcache`, plus a `supported Python binding
  <https://memcached.org/>`_
* `gettext <https://www.gnu.org/software/gettext/manual/gettext.html>`_
  (:ref:`gettext_on_windows`)
* :pypi:`selenium` 4.23.0+
* :pypi:`sqlparse` 0.5.0+ (required)
* :pypi:`tblib` 3.0.0+

You can find these dependencies in `pip requirements files
<https://pip.pypa.io/en/latest/user_guide/#requirements-files>`_ inside the
``tests/requirements`` directory of the Django source tree and install them
like so:

.. console::

   $ python -m pip install -r tests/requirements/py3.txt

If you encounter an error during the installation, your system might be missing
a dependency for one or more of the Python packages. Consult the failing
package's documentation or search the web with the error message that you
encounter.

You can also install the database adapter(s) of your choice using
``oracle.txt``, ``mysql.txt``, or ``postgres.txt``.

If you want to test the memcached or Redis cache backends, you'll also need to
define a :setting:`CACHES` setting that points at your memcached or Redis
instance respectively.

To run the GeoDjango tests, you will need to :doc:`set up a spatial database
and install the Geospatial libraries</ref/contrib/gis/install/index>`.

Each of these dependencies is optional. If you're missing any of them, the
associated tests will be skipped.

To run some of the autoreload tests, you'll need to install the
`Watchman <https://facebook.github.io/watchman/>`_ service.

Code coverage
-------------

Contributors are encouraged to run coverage on the test suite to identify areas
that need additional tests. The coverage tool installation and use is described
in :ref:`testing code coverage<topics-testing-code-coverage>`.

To run coverage on the Django test suite using the standard test settings:

.. console::

   $ coverage run ./runtests.py --settings=test_sqlite

After running coverage, combine all coverage statistics by running:

.. console::

   $ coverage combine

After that generate the html report by running:

.. console::

   $ coverage html

When running coverage for the Django tests, the included ``.coveragerc``
settings file  defines ``coverage_html`` as the output directory for the report
and also excludes several directories not relevant to the results
(test code or external code included in Django).

.. _contrib-apps:

Contrib apps
============

Tests for contrib apps can be found in the :source:`tests/` directory, typically
under ``<app_name>_tests``. For example, tests for ``contrib.auth`` are located
in :source:`tests/auth_tests`.

.. _troubleshooting-unit-tests:

Troubleshooting
===============

Test suite hangs or shows failures on ``main`` branch
-----------------------------------------------------

Ensure you have the latest point release of a :ref:`supported Python version
<faq-python-version-support>`, since there are often bugs in earlier versions
that may cause the test suite to fail or hang.

On **macOS** (High Sierra and newer versions), you might see this message
logged, after which the tests hang:

.. code-block:: pytb

    objc[42074]: +[__NSPlaceholderDate initialize] may have been in progress in
    another thread when fork() was called.

To avoid this set a ``OBJC_DISABLE_INITIALIZE_FORK_SAFETY`` environment
variable, for example:

.. code-block:: shell

    $ OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES ./runtests.py

Or add ``export OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES`` to your shell's
startup file (e.g. ``~/.profile``).

Many test failures with ``UnicodeEncodeError``
----------------------------------------------

If the ``locales`` package is not installed, some tests will fail with a
``UnicodeEncodeError``.

You can resolve this on Debian-based systems, for example, by running:

.. code-block:: console

    $ apt-get install locales
    $ dpkg-reconfigure locales

You can resolve this for macOS systems by configuring your shell's locale:

.. code-block:: console

    $ export LANG="en_US.UTF-8"
    $ export LC_ALL="en_US.UTF-8"

Run the ``locale`` command to confirm the change. Optionally, add those export
commands to your shell's startup file (e.g. ``~/.bashrc`` for Bash) to avoid
having to retype them.

Tests that only fail in combination
-----------------------------------

In case a test passes when run in isolation but fails within the whole suite,
we have some tools to help analyze the problem.

The ``--bisect`` option of ``runtests.py`` will run the failing test while
halving the test set it is run together with on each iteration, often making
it possible to identify a small number of tests that may be related to the
failure.

For example, suppose that the failing test that works on its own is
``ModelTest.test_eq``, then using:

.. console::

    $ ./runtests.py --bisect basic.tests.ModelTest.test_eq

will try to determine a test that interferes with the given one. First, the
test is run with the first half of the test suite. If a failure occurs, the
first half of the test suite is split in two groups and each group is then run
with the specified test. If there is no failure with the first half of the test
suite, the second half of the test suite is run with the specified test and
split appropriately as described earlier. The process repeats until the set of
failing tests is minimized.

The ``--pair`` option runs the given test alongside every other test from the
suite, letting you check if another test has side-effects that cause the
failure. So:

.. console::

    $ ./runtests.py --pair basic.tests.ModelTest.test_eq

will pair ``test_eq`` with every test label.

With both ``--bisect`` and ``--pair``, if you already suspect which cases
might be responsible for the failure, you may limit tests to be cross-analyzed
by :ref:`specifying further test labels <runtests-specifying-labels>` after
the first one:

.. console::

    $ ./runtests.py --pair basic.tests.ModelTest.test_eq queries transactions

You can also try running any set of tests in a random or reverse order using
the ``--shuffle`` and ``--reverse`` options. This can help verify that
executing tests in a different order does not cause any trouble:

.. console::

    $ ./runtests.py basic --shuffle
    $ ./runtests.py basic --reverse

Seeing the SQL queries run during a test
----------------------------------------

If you wish to examine the SQL being run in failing tests, you can turn on
:ref:`SQL logging <django-db-logger>` using the ``--debug-sql`` option. If you
combine this with ``--verbosity=2``, all SQL queries will be output:

.. console::

    $ ./runtests.py basic --debug-sql

Seeing the full traceback of a test failure
-------------------------------------------

By default tests are run in parallel with one process per core. When the tests
are run in parallel, however, you'll only see a truncated traceback for any
test failures. You can adjust this behavior with the ``--parallel`` option:

.. console::

    $ ./runtests.py basic --parallel=1

You can also use the :envvar:`DJANGO_TEST_PROCESSES` environment variable for
this purpose.

Tips for writing tests
======================

Isolating model registration
----------------------------

To avoid polluting the global :attr:`~django.apps.apps` registry and prevent
unnecessary table creation, models defined in a test method should be bound to
a temporary ``Apps`` instance. To do this, use the
:func:`~django.test.utils.isolate_apps` decorator::

    from django.db import models
    from django.test import SimpleTestCase
    from django.test.utils import isolate_apps


    class TestModelDefinition(SimpleTestCase):
        @isolate_apps("app_label")
        def test_model_definition(self):
            class TestModel(models.Model):
                pass

            ...

.. admonition:: Setting ``app_label``

    Models defined in a test method with no explicit
    :attr:`~django.db.models.Options.app_label` are automatically assigned the
    label of the app in which their test class is located.

    In order to make sure the models defined within the context of
    :func:`~django.test.utils.isolate_apps` instances are correctly
    installed, you should pass the set of targeted ``app_label`` as arguments:

    .. code-block:: python
        :caption: ``tests/app_label/tests.py``

        from django.db import models
        from django.test import SimpleTestCase
        from django.test.utils import isolate_apps


        class TestModelDefinition(SimpleTestCase):
            @isolate_apps("app_label", "other_app_label")
            def test_model_definition(self):
                # This model automatically receives app_label='app_label'
                class TestModel(models.Model):
                    pass

                class OtherAppModel(models.Model):
                    class Meta:
                        app_label = "other_app_label"

                ...