Refs #25050 -- Corrected test assertion in serializers test.

tests/serializers/tests.py

@@ -229,7 +229,9 @@ class SerializersTestBase(object):
         author = Author.objects.defer('name').get(pk=author.pk)
         serial_str = serializers.serialize(self.serializer_name, [author])
         deserial_objs = list(serializers.deserialize(self.serializer_name, serial_str))
-        self.assertIsInstance(deserial_objs[0].object, Author)
+        # Check the class instead of using isinstance() because model instances
+        # with deferred fields (e.g. Author_Deferred_name) will pass isinstance.
+        self.assertEqual(deserial_objs[0].object.__class__, Author)
 
     def test_custom_field_serialization(self):
         """Tests that custom fields serialize and deserialize intact"""