      backend = 'django.contrib.auth.tests.test_remote_user.RemoteUserNoCreateBackend'
  
      def test_unknown_user(self):
          num_users = User.objects.count()
          response = self.client.get('/remote_user/', REMOTE_USER='newuser')
          self.assertTrue(response.context['user'].is_anonymous())
          self.assertEqual(User.objects.count(), num_users)
  
  
  class CustomRemoteUserBackend(RemoteUserBackend):
 
</s> remove         response = self.client.get('/remote_user/', REMOTE_USER='')
 </s> add         response = self.client.get('/remote_user/', **{self.header: ''}) </s> remove         response = self.client.get('/remote_user/', REMOTE_USER=None)
 </s> add         response = self.client.get('/remote_user/', **{self.header: None}) </s> remove         response = self.client.get('/remote_user/', REMOTE_USER='newuser')
 </s> add         response = self.client.get('/remote_user/', **{self.header: 'newuser'}) </s> remove         response = self.client.get('/remote_user/', REMOTE_USER=self.known_user)
 </s> add         response = self.client.get('/remote_user/',
                                   **{self.header: self.known_user}) </s> remove         response = self.client.get('/remote_user/', REMOTE_USER='newuser')
 </s> add         response = self.client.get('/remote_user/', **{self.header: 'newuser'})
        response = self.client.get('/remote_user/', **{self.header: 'newuser'})
      backend = 'django.contrib.auth.tests.test_remote_user.RemoteUserNoCreateBackend'
  
      def test_unknown_user(self):
          num_users = User.objects.count()
        response = self.client.get('/remote_user/', **{self.header: 'newuser'})
          self.assertTrue(response.context['user'].is_anonymous())
          self.assertEqual(User.objects.count(), num_users)
  
  
  class CustomRemoteUserBackend(RemoteUserBackend):
keep keep keep keep replace keep keep keep keep keep
 Fixed #21250 -- Made HTTP auth user header configurable in tests

Currently, if the authentication mechanism uses a custom HTTP header
and not REMOTE_USER, it is not easy to test. This commit modifies
remote user tests in order to make them more generic. 
django/contrib/auth/tests/test_remote_user.py