Fixed running auth_tests in isolation after 3a47d42f.

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"