Second fix for PYTHON-1044

Author: nick

cassandra/cluster.py

@@ -3730,6 +3730,7 @@ def _on_timeout(self, _attempts=0):
                 key = "Connection defunct by heartbeat"
                 errors = {key: "Client request timeout. See Session.execute[_async](timeout)"}
                 self._set_final_exception(OperationTimedOut(errors, self._current_host))
+                return
 
             pool = self.session._pools.get(self._current_host)
             if pool and not pool.is_shutdown:

tests/unit/test_response_future.py

@@ -156,7 +156,7 @@ def test_heartbeat_defunct_deadlock(self):
 
         # Simulate ResponseFuture timing out
         rf._on_timeout()
-        self.assertRaises(OperationTimedOut, rf.result)
+        self.assertRaisesRegexp(OperationTimedOut, "Connection defunct by heartbeat", rf.result)
 
     def test_read_timeout_error_message(self):
         session = self.make_session()