add todo comment

Author: Yancey0623

tests/mock_servicer.py

@@ -21,6 +21,7 @@ def Run(self, request, context):
                 for res in MockServicer.table_response(MockServicer.get_test_table()):
                     yield res
         elif SQL == "TEST VERIFY SESSION":
+            # TODO(Yancey1989): using a elegant way to test the session instead of the trick.
             yield MockServicer.message_response("|".join([request.session.token, request.session.db_conn_str]))
         else:
             yield MockServicer.message_response('bad request', 0)