Removed direct manipulation of settings in auth tests; refs #21230.

django/contrib/auth/tests/test_auth_backends.py

 from __future__ import unicode_literals
 from datetime import date
 
-from django.conf import settings
 from django.contrib.auth.backends import ModelBackend
 from django.contrib.auth.models import User, Group, Permission, AnonymousUser
 from django.contrib.auth.tests.utils import skipIfCustomUser
@@ -34,12 +33,14 @@ class BaseModelBackendTest(object):
     backend = 'django.contrib.auth.backends.ModelBackend'
 
     def setUp(self):
-        self.curr_auth = list(settings.AUTHENTICATION_BACKENDS)
-        settings.AUTHENTICATION_BACKENDS = [self.backend]
+        self.patched_settings = modify_settings(
+            AUTHENTICATION_BACKENDS={'append': self.backend},
+        )
+        self.patched_settings.enable()
         self.create_users()
 
     def tearDown(self):
-        settings.AUTHENTICATION_BACKENDS = self.curr_auth
+        self.patched_settings.disable()
         # The custom_perms test messes with ContentTypes, which will
         # be cached; flush the cache to ensure there are no side effects
         # Refs #14975, #14925

django/contrib/auth/tests/test_remote_user.py

@@ -6,7 +6,7 @@ from django.contrib.auth.backends import RemoteUserBackend
 from django.contrib.auth.middleware import RemoteUserMiddleware
 from django.contrib.auth.models import User
 from django.contrib.auth.tests.utils import skipIfCustomUser
-from django.test import TestCase, override_settings
+from django.test import TestCase, modify_settings, override_settings
 from django.utils import timezone
 
 
@@ -23,15 +23,14 @@ class RemoteUserTest(TestCase):
     known_user2 = 'knownuser2'
 
     def setUp(self):
-        self.curr_middleware = list(settings.MIDDLEWARE_CLASSES)
-        self.curr_auth = list(settings.AUTHENTICATION_BACKENDS)
-        settings.MIDDLEWARE_CLASSES = settings.MIDDLEWARE_CLASSES + [self.middleware]
-        settings.AUTHENTICATION_BACKENDS = settings.AUTHENTICATION_BACKENDS + [self.backend]
+        self.patched_settings = modify_settings(
+            AUTHENTICATION_BACKENDS={'append': self.backend},
+            MIDDLEWARE_CLASSES={'append': self.middleware},
+        )
+        self.patched_settings.enable()
 
     def tearDown(self):
-        """Restores settings to avoid breaking other tests."""
-        settings.MIDDLEWARE_CLASSES = self.curr_middleware
-        settings.AUTHENTICATION_BACKENDS = self.curr_auth
+        self.patched_settings.disable()
 
     def test_no_remote_user(self):
         """