django/tests/deprecation/test_middleware_mixin.py

from django.contrib.sessions.middleware import SessionMiddleware
from django.middleware.cache import (
    CacheMiddleware, FetchFromCacheMiddleware, UpdateCacheMiddleware,
)
from django.middleware.common import CommonMiddleware
from django.middleware.security import SecurityMiddleware
from django.test import SimpleTestCase
from django.utils.deprecation import RemovedInDjango40Warning


class MiddlewareMixinTests(SimpleTestCase):
    """
    Deprecation warning is raised when using get_response=None.
    """
    msg = 'Passing None for the middleware get_response argument is deprecated.'

    def test_deprecation(self):
        with self.assertRaisesMessage(RemovedInDjango40Warning, self.msg):
            CommonMiddleware()

    def test_passing_explicit_none(self):
        with self.assertRaisesMessage(RemovedInDjango40Warning, self.msg):
            CommonMiddleware(None)

    def test_subclass_deprecation(self):
        """
        Deprecation warning is raised in subclasses overriding __init__()
        without calling super().
        """
        for middleware in [
            SessionMiddleware,
            CacheMiddleware,
            FetchFromCacheMiddleware,
            UpdateCacheMiddleware,
            SecurityMiddleware,
        ]:
            with self.subTest(middleware=middleware):
                with self.assertRaisesMessage(RemovedInDjango40Warning, self.msg):
                    middleware()