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

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

.. highlight:: console

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
----------

If you are on Python 2, you'll first need to install a backport of the
``unittest.mock`` module that's available in Python 3. See
:ref:`running-unit-tests-dependencies` for details on installing `mock`_ and
the other optional test dependencies.

Running the tests requires a Django settings module that defines the
databases to use. To make it easy to get started, Django provides and uses a
sample settings module that uses the SQLite database. To run the tests::

   $ git clone https://github.com/django/django.git django-repo
   $ cd django-repo/tests
   $ PYTHONPATH=..:$PYTHONPATH ./runtests.py

.. admonition:: Windows users

    We recommend something like `Git Bash <https://msysgit.github.io/>`_ to run
    the tests using the above approach.

You can avoid typing the ``PYTHONPATH`` bit each time by adding your Django
checkout to your ``PYTHONPATH`` or by installing the source checkout using pip.
See :ref:`installing-development-version`.

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

.. _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.

To run the tests with different settings, ensure that the module is on your
``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::

   $ ./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 just want to run 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::

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

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

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

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

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

   $ ./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.

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

.. _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:

*  argon2-cffi_ 16.0.0+
*  bcrypt_
*  docutils_
*  enum34_ (Python 2 only)
*  geoip2_
*  jinja2_ 2.7+
*  numpy_
*  Pillow_
*  PyYAML_
*  pytz_
*  setuptools_
*  memcached_, plus a :ref:`supported Python binding <memcached>`
*  mock_ (for Python 2)
*  gettext_ (:ref:`gettext_on_windows`)
*  selenium_
*  sqlparse_

You can find these dependencies in `pip requirements files`_ inside the
``tests/requirements`` directory of the Django source tree and install them
like so::

   $ pip install -r tests/requirements/py3.txt  # Python 2: py2.txt

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 cache backend, you'll also need to define
a :setting:`CACHES` setting that points at your memcached instance.

To run the GeoDjango tests, you will need to :doc:`setup 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.

.. _argon2-cffi: https://pypi.python.org/pypi/argon2_cffi
.. _bcrypt: https://pypi.python.org/pypi/bcrypt
.. _docutils: https://pypi.python.org/pypi/docutils
.. _enum34: https://pypi.python.org/pypi/enum34
.. _geoip2: https://pypi.python.org/pypi/geoip2
.. _jinja2: https://pypi.python.org/pypi/jinja2
.. _numpy: https://pypi.python.org/pypi/numpy
.. _Pillow: https://pypi.python.org/pypi/Pillow/
.. _PyYAML: http://pyyaml.org/wiki/PyYAML
.. _pytz: https://pypi.python.org/pypi/pytz/
.. _setuptools: https://pypi.python.org/pypi/setuptools/
.. _memcached: http://memcached.org/
.. _mock: https://pypi.python.org/pypi/mock
.. _gettext: https://www.gnu.org/software/gettext/manual/gettext.html
.. _selenium: https://pypi.python.org/pypi/selenium
.. _sqlparse: https://pypi.python.org/pypi/sqlparse
.. _pip requirements files: https://pip.pypa.io/en/latest/user_guide.html#requirements-files

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>`.

Coverage should be run in a single process to obtain accurate statistics. To
run coverage on the Django test suite using the standard test settings::

   $ coverage run ./runtests.py --settings=test_sqlite --parallel=1

After running coverage, generate the html report by running::

   $ 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 ``tests/`` directory, typically
under ``<app_name>_tests``. For example, tests for ``contrib.auth`` are located
in ``tests/auth_tests``.

.. _troubleshooting-unit-tests:

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

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::

    $ apt-get install locales
    $ dpkg-reconfigure locales

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::

    $ ./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::

    $ ./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::

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

You can also try running any set of tests in reverse using the ``--reverse``
option in order to verify that executing tests in a different order does not
cause any trouble::

    $ ./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::

    $ ./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::

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

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

.. versionadded:: 1.9

    Support for running tests in parallel and the ``--parallel`` option were
    added.

Tips for writing tests
----------------------

.. highlight:: python

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::

    from django.apps.registry import Apps
    from django.db import models
    from django.test import SimpleTestCase

    class TestModelDefinition(SimpleTestCase):
        def test_model_definition(self):
            test_apps = Apps(['app_label'])

            class TestModel(models.Model):
                class Meta:
                    apps = test_apps
            ...

.. function:: django.test.utils.isolate_apps(*app_labels, attr_name=None, kwarg_name=None)

.. versionadded:: 1.10

Since this pattern involves a lot of boilerplate, Django provides the
:func:`~django.test.utils.isolate_apps` decorator. It's used like this::

    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:

    .. snippet::
        :filename: 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'
                ...

The decorator can also be applied to classes::

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

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

The temporary ``Apps`` instance used to isolate model registration can be
retrieved as an attribute when used as a class decorator by using the
``attr_name`` parameter::

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

    @isolate_apps('app_label', attr_name='apps')
    class TestModelDefinition(SimpleTestCase):
        def test_model_definition(self):
            class TestModel(models.Model):
                pass
            self.assertIs(self.apps.get_model('app_label', 'TestModel'), TestModel)

Or as an argument on the test method when used as a method decorator by using
the ``kwarg_name`` parameter::

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

    class TestModelDefinition(SimpleTestCase):
        @isolate_apps('app_label', kwarg_name='apps')
        def test_model_definition(self, apps):
            class TestModel(models.Model):
                pass
            self.assertIs(apps.get_model('app_label', 'TestModel'), TestModel)