def test_customer_subscriber_fk_fallback_to_auth_user_model(self):
        """
        Test to ensure customer.subscriber fk points to the fallback AUTH_USER_MODEL
        when DJSTRIPE_SUBSCRIBER_MODEL is not set
        """
        # assert DJSTRIPE_SUBSCRIBER_MODEL has not been set
        with pytest.raises(AttributeError):
            settings.DJSTRIPE_SUBSCRIBER_MODEL

        field = Customer._meta.get_field("subscriber")
        self.assertEqual(field.related_model, get_user_model())

        Test to ensure customer.subscriber fk points to the fallback AUTH_USER_MODEL
        when DJSTRIPE_SUBSCRIBER_MODEL is not set
        
tests/test_migrations.py