Cleared get_models cache when swapping User model.

Thanks Florian for isolating the shortest way to reproduce this issue:

./runtests.py \
    django.contrib.auth.tests.test_context_processors.AuthContextProcessorTests.test_perms_attrs \
    django.contrib.auth.tests.test_auth_backends.ChangedBackendSettingsTest.test_changed_backend_settings \
    django.contrib.auth.tests.test_auth_backends.CustomUserModelBackendAuthenticateTest.test_authenticate \
    django.contrib.auth.tests.test_basic.BasicTestCase.test_createsuperuser_management_command

1 files changed, 2 insertions, 0 deletions

diff --git a/django/contrib/auth/tests/test_basic.py b/django/contrib/auth/tests/test_basic.py
index ec33aece25..beaa97f285 100644
--- a/django/contrib/auth/tests/test_basic.py
+++ b/django/contrib/auth/tests/test_basic.py
@@ -3,6 +3,7 @@ from __future__ import unicode_literals
 
 import locale
 
+from django.apps import apps
 from django.contrib.auth import get_user_model
 from django.contrib.auth.management.commands import createsuperuser
 from django.contrib.auth.models import User, AnonymousUser
@@ -25,6 +26,7 @@ def user_model_swapped(**kwargs):
         # Reset User manager
         setattr(User, 'objects', User._default_manager)
         ensure_default_manager(User)
+        apps.get_models.cache_clear()
 
 
 def mock_inputs(inputs):