# Τεκμηρίωση του Django - 1.10.7

# Advanced testing topics

## The request factory

class `RequestFactory`

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 `follows`. 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 TestCase, RequestFactory

    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 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`

  Προειδοποίηση

  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 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:

  - `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 an 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 tests that were found.
6. Destroying the test databases.
7. 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_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. Grouping by test class is preserved when using this option.

  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)

  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)

  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)

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

`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.

`DiscoverRunner.``setup_databases`(**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 `teardown_databases()` function at the conclusion of testing.

`DiscoverRunner.``run_suite`(suite, **kwargs)

  Runs the test suite.

  Returns the result produced by the running the test suite.

`DiscoverRunner.``teardown_databases`(old_config, **kwargs)

  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 is the return value of the `setup_databases()` method.

`DiscoverRunner.``teardown_test_environment`(**kwargs)

  Restores the pre-test environment.

`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`

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`()

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

`teardown_test_environment`()

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

#### `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.