Writing and running tests¶
This document is split into two primary sections. First, we explain how to write tests with Django. Then, we explain how to run them.
Django’s unit tests use a Python standard library module:
module defines tests using a class-based approach.
from django.test import TestCase from myapp.models import Animal class AnimalTestCase(TestCase): def setUp(self): Animal.objects.create(name="lion", sound="roar") Animal.objects.create(name="cat", sound="meow") def test_animals_can_speak(self): """Animals that can speak are correctly identified""" lion = Animal.objects.get(name="lion") cat = Animal.objects.get(name="cat") self.assertEqual(lion.speak(), 'The lion says "roar"') self.assertEqual(cat.speak(), 'The cat says "meow"')
When you run your tests, the default behavior of the
test utility is to find all the test cases (that is, subclasses of
unittest.TestCase) in any file whose name begins with
automatically build a test suite out of those test cases, and run that suite.
For more details about
unittest, see the Python documentation.
Where should the tests live?
startapp template creates a
tests.py file in the
new application. This might be fine if you only have a few tests, but as
your test suite grows you’ll likely want to restructure it into a tests
package so you can split your tests into different submodules such as
test_forms.py, etc. Feel free to
pick whatever organizational scheme you like.
unittest.TestCase avoids the cost of running each test in a
transaction and flushing the database, but if your tests interact with
the database their behavior will vary based on the order that the test
runner executes them. This can lead to unit tests that pass when run in
isolation but fail when run in a suite.
Once you’ve written tests, run them using the
test command of
$ ./manage.py test
Test discovery is based on the unittest module’s built-in test
discovery. By default, this will discover tests in
any file named
test*.py under the current working directory.
You can specify particular tests to run by supplying any number of “test
./manage.py test. Each test label can be a full Python dotted
path to a package, module,
TestCase subclass, or test method. For instance:
# Run all the tests in the animals.tests module $ ./manage.py test animals.tests # Run all the tests found within the 'animals' package $ ./manage.py test animals # Run just one test case $ ./manage.py test animals.tests.AnimalTestCase # Run just one test method $ ./manage.py test animals.tests.AnimalTestCase.test_animals_can_speak
You can also provide a path to a directory to discover tests below that directory:
$ ./manage.py test animals/
You can specify a custom filename pattern match using the
--pattern) option, if your test files are named differently from the
$ ./manage.py test --pattern="tests_*.py"
If you press
Ctrl-C while the tests are running, the test runner will
wait for the currently running test to complete and then exit gracefully.
During a graceful exit the test runner will output details of any test
failures, report on how many tests were run and how many errors and failures
were encountered, and destroy any test databases as usual. Thus pressing
Ctrl-C can be very useful if you forget to pass the
--failfast option, notice that some tests are unexpectedly failing and
want to get details on the failures without waiting for the full test run to
If you do not want to wait for the currently running test to finish, you
Ctrl-C a second time and the test run will halt immediately,
but not gracefully. No details of the tests run before the interruption will
be reported, and any test databases created by the run will not be destroyed.
Test with warnings enabled
It’s a good idea to run your tests with Python warnings enabled:
python -Wa manage.py test. The
-Wa flag tells Python to
display deprecation warnings. Django, like many other Python libraries,
uses these warnings to flag when features are going away. It also might
flag areas in your code that aren’t strictly wrong but could benefit
from a better implementation.
The test database¶
Tests that require a database (namely, model tests) will not use your “real” (production) database. Separate, blank databases are created for the tests.
Regardless of whether the tests pass or fail, the test databases are destroyed when all the tests have been executed.
You can prevent the test databases from being destroyed by using the
test --keepdb option. This will preserve the test database between
runs. If the database does not exist, it will first be created. Any migrations
will also be applied in order to keep it up to date.
As described in the previous section, if a test run is forcefully interrupted,
the test database may not be destroyed. On the next run, you’ll be asked
whether you want to reuse or destroy the database. Use the
--noinput option to suppress that prompt and automatically destroy the
database. This can be useful when running tests on a continuous integration
server where tests may be interrupted by a timeout, for example.
The default test database names are created by prepending
test_ to the
value of each
DATABASES. When using SQLite, the
tests will use an in-memory database by default (i.e., the database will be
created in memory, bypassing the filesystem entirely!). The
TEST dictionary in
DATABASES offers a number of settings
to configure your test database. For example, if you want to use a different
database name, specify
NAME in the
TEST dictionary for any given database in
USER will also need read access to the built-in
Aside from using a separate database, the test runner will otherwise
use all of the same database settings you have in your settings file:
HOST, etc. The
test database is created by the user specified by
USER, so you’ll
need to make sure that the given user account has sufficient privileges to
create a new database on the system.
For fine-grained control over the character encoding of your test
database, use the
CHARSET TEST option. If you’re using
MySQL, you can also use the
COLLATION option to
control the particular collation used by the test database. See the
settings documentation for details of these
and other advanced settings.
If using an SQLite in-memory database with SQLite, shared cache is enabled, so you can write tests with ability to share the database between threads.
Finding data from your production database when running tests?
If your code attempts to access the database when its modules are compiled, this will occur before the test database is set up, with potentially unexpected results. For example, if you have a database query in module-level code and a real database exists, production data could pollute your tests. It is a bad idea to have such import-time database queries in your code anyway - rewrite your code so that it doesn’t do this.
This also applies to customized implementations of
Order in which tests are executed¶
In order to guarantee that all
TestCase code starts with a clean database,
the Django test runner reorders tests in the following way:
TestCasesubclasses are run first.
- Then, all other Django-based tests (test cases based on
TransactionTestCase) are run with no particular ordering guaranteed nor enforced among them.
- Then any other
unittest.TestCasetests (including doctests) that may alter the database without restoring it to its original state are run.
The new ordering of tests may reveal unexpected dependencies on test case
ordering. This is the case with doctests that relied on state left in the
database by a given
TransactionTestCase test, they
must be updated to be able to run independently.
Failures detected when loading tests are ordered before all of the above for quicker feedback. This includes things like test modules that couldn’t be found or that couldn’t be loaded due to syntax errors.
Any initial data loaded in migrations will only be available in
tests and not in
TransactionTestCase tests, and additionally only on
backends where transactions are supported (the most important exception being
MyISAM). This is also true for tests which rely on
Django can reload that data for you on a per-testcase basis by
serialized_rollback option to
True in the body of the
TransactionTestCase, but note that this will slow down
that test suite by approximately 3x.
Third-party apps or those developing against MyISAM will need to set this;
in general, however, you should be developing your own projects against a
transactional database and be using
TestCase for most tests, and thus
not need this setting.
The initial serialization is usually very quick, but if you wish to exclude
some apps from this process (and speed up test runs slightly), you may add
those apps to
To prevent serialized data from being loaded twice, setting
serialized_rollback=True disables the
post_migrate signal when flushing the test
Other test conditions¶
Regardless of the value of the
DEBUG setting in your configuration
file, all Django tests run with
DEBUG=False. This is to ensure that
the observed output of your code matches what will be seen in a production
Caches are not cleared after each test, and running
manage.py test fooapp
can insert data from the tests into the cache of a live system if you run your
tests in production because, unlike databases, a separate “test cache” is not
used. This behavior may change in the future.
Understanding the test output¶
When you run your tests, you’ll see a number of messages as the test runner
prepares itself. You can control the level of detail of these messages with the
verbosity option on the command line:
Creating test database... Creating table myapp_animal Creating table myapp_mineral
This tells you that the test runner is creating a test database, as described in the previous section.
Once the test database has been created, Django will run your tests. If everything goes well, you’ll see something like this:
---------------------------------------------------------------------- Ran 22 tests in 0.221s OK
If there are test failures, however, you’ll see full details about which tests failed:
====================================================================== FAIL: test_was_published_recently_with_future_poll (polls.tests.PollMethodTests) ---------------------------------------------------------------------- Traceback (most recent call last): File "/dev/mysite/polls/tests.py", line 16, in test_was_published_recently_with_future_poll self.assertIs(future_poll.was_published_recently(), False) AssertionError: True is not False ---------------------------------------------------------------------- Ran 1 test in 0.003s FAILED (failures=1)
A full explanation of this error output is beyond the scope of this document,
but it’s pretty intuitive. You can consult the documentation of Python’s
unittest library for details.
Note that the return code for the test-runner script is 1 for any number of failed tests (whether the failure was caused by an error, a failed assertion, or an unexpected success). If all the tests pass, the return code is 0. This feature is useful if you’re using the test-runner script in a shell script and need to test for success or failure at that level.
Speeding up the tests¶
Running tests in parallel¶
As long as your tests are properly isolated, you can run them in parallel to
gain a speed up on multi-core hardware. See
The default password hasher is rather slow by design. If you’re authenticating
many users in your tests, you may want to use a custom settings file and set
PASSWORD_HASHERS setting to a faster hashing algorithm:
PASSWORD_HASHERS = [ 'django.contrib.auth.hashers.MD5PasswordHasher', ]
Don’t forget to also include in
PASSWORD_HASHERS any hashing
algorithm used in fixtures, if any.
Preserving the test database¶
test --keepdb option preserves the test database between test
runs. It skips the create and destroy actions which can greatly decrease the
time to run tests.