Refs #35402 -- Added tests for invalid usage of submodules in some settings.

tests/auth_tests/test_models.py

@@ -433,6 +433,13 @@ class UserWithPermTestCase(TestCase):
                 backend="invalid.backend.CustomModelBackend",
             )
 
+    def test_invalid_backend_submodule(self):
+        with self.assertRaises(ImportError):
+            User.objects.with_perm(
+                "auth.test",
+                backend="json.tool",
+            )
+
     @override_settings(
         AUTHENTICATION_BACKENDS=["auth_tests.test_models.CustomModelBackend"]
     )