Advanced testing topics

The request factory

class RequestFactory[source]

The 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 RequestFactory is a slightly restricted subset of the test client API:

  • It only has access to the HTTP methods get(), post(), put(), delete(), head(), options(), and 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)

Tests and multiple host names

The 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 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 ALLOWED_HOSTS using override_settings() or 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 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.

Tests and multiple databases

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 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.

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 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 DEPENDENCIES definition, an ImproperlyConfigured exception will be raised.

Advanced features of TransactionTestCase

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 flush to reset the database state. This empties all tables and emits the post_migrate signal, which recreates one content type and four 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:

  • 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 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 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 post_migrate. Considering the order in which tests are executed, 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.

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.

Using the Django test runner to test reusable applications

If you are writing a reusable application 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:

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.

tests/test_settings.py
SECRET_KEY = 'fake-key'
INSTALLED_APPS = [
    "tests",
]

This file contains the Django 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 INSTALLED_APPS when running your tests, you can define test-only models in its models.py file.

Using different testing frameworks

Clearly, 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 TEST_RUNNER setting to determine what to do. By default, TEST_RUNNER points to 'django.test.runner.DiscoverRunner'. This class defines the default Django testing behavior. This behavior involves:

  1. Performing global pre-test setup.
  2. Looking for tests in any file below the current directory whose name matches the pattern test*.py.
  3. Creating the test databases.
  4. Running migrate to install models and initial data into the test databases.
  5. Running the system checks.
  6. Running the tests that were found.
  7. Destroying the test databases.
  8. Performing global post-test teardown.

If you define your own test runner class and point 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.

Defining a 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)[source]

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. Grouping by test class is preserved when using this option.

debug_mode specifies what the 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 django.db.backends 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 test command will be able to use those arguments.

Attributes

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.

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.

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

DiscoverRunner.run_tests(test_labels, extra_tests=None, **kwargs)[source]

Run the test suite.

test_labels allows you to specify which tests to run and supports several formats (see 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)[source]

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

DiscoverRunner.setup_test_environment(**kwargs)[source]

Sets up the test environment by calling setup_test_environment() and setting DEBUG to self.debug_mode (defaults to False).

DiscoverRunner.build_suite(test_labels, extra_tests=None, **kwargs)[source]

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.

DiscoverRunner.setup_databases(**kwargs)[source]

Creates the test databases by calling setup_databases().

DiscoverRunner.run_checks()[source]

Runs the system checks.

DiscoverRunner.run_suite(suite, **kwargs)[source]

Runs the test suite.

Returns the result produced by the running the test suite.

DiscoverRunner.get_test_runner_kwargs()[source]

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

DiscoverRunner.teardown_databases(old_config, **kwargs)[source]

Destroys the test databases, restoring pre-test conditions by calling teardown_databases().

DiscoverRunner.teardown_test_environment(**kwargs)[source]

Restores the pre-test environment.

DiscoverRunner.suite_result(suite, result, **kwargs)[source]

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

Testing utilities

django.test.utils

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

setup_test_environment(debug=None)[source]

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 DEBUG setting is updated to its value.

teardown_test_environment()[source]

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

setup_databases(verbosity, interactive, keepdb=False, debug_sql=False, parallel=0, **kwargs)[source]

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 teardown_databases() function at the conclusion of testing.

teardown_databases(old_config, parallel=0, keepdb=False)[source]

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 setup_databases() method.

django.db.connection.creation

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

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 serialized_rollback=True.

If you are using the default test runner, you can control this with the the SERIALIZE entry in the 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 NAME in DATABASES to match the name of the test database.

destroy_test_db(old_database_name, verbosity=1, keepdb=False)

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

The verbosity argument has the same behavior as for DiscoverRunner.

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

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.

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