Fixed #21281 -- Made override_settings act at class level when used as a TestCase decorator.

tests/cache/tests.py

@@ -28,6 +28,7 @@ from django.middleware.csrf import CsrfViewMiddleware
 from django.template import Template
 from django.template.response import TemplateResponse
 from django.test import TestCase, TransactionTestCase, RequestFactory, override_settings
+from django.test.signals import setting_changed
 from django.test.utils import IgnoreDeprecationWarningsMixin
 from django.utils import six
 from django.utils import timezone
@@ -1144,8 +1145,12 @@ class FileBasedCacheTests(BaseCacheTests, TestCase):
     def setUp(self):
         super(FileBasedCacheTests, self).setUp()
         self.dirname = tempfile.mkdtemp()
+        # Caches location cannot be modified through override_settings / modify_settings,
+        # hence settings are manipulated directly here and the setting_changed signal
+        # is triggered manually.
         for cache_params in settings.CACHES.values():
             cache_params.update({'LOCATION': self.dirname})
+        setting_changed.send(self.__class__, setting='CACHES', enter=False)
 
     def tearDown(self):
         super(FileBasedCacheTests, self).tearDown()