Fixed running auth_tests in isolation after 3a47d42f.

tests/auth_tests/test_basic.py

@@ -3,16 +3,25 @@ from __future__ import unicode_literals
 
 import warnings
 
+from django.apps import apps
 from django.contrib.auth import get_user_model
 from django.contrib.auth.models import AnonymousUser, User
 from django.core.exceptions import ImproperlyConfigured
 from django.db import IntegrityError
+from django.dispatch import receiver
 from django.test import TestCase, override_settings
+from django.test.signals import setting_changed
 from django.utils import translation
 
 from .models import CustomUser
 
 
+@receiver(setting_changed)
+def user_model_swapped(**kwargs):
+    if kwargs['setting'] == 'AUTH_USER_MODEL':
+        apps.clear_cache()
+
+
 class BasicTestCase(TestCase):
     def test_user(self):
         "Check that users can be created and can set their password"