diff --git a/tests/unit/test_concurrent.py b/tests/unit/test_concurrent.py
index 3c2734e4..d120cd4a 100644
--- a/tests/unit/test_concurrent.py
+++ b/tests/unit/test_concurrent.py
@@ -33,6 +33,7 @@ class MockResponseResponseFuture():
     """
 
     _query_trace = None
+    _col_names = None
 
     # a list pending callbacks, these will be prioritized in reverse or normal orderd
     pending_callbacks = PriorityQueue()