Mock heartbeat thread start/stop in coordinator fixture

Author: dpkp

test/test_coordinator.py

@@ -400,6 +400,8 @@ def patched_coord(mocker, coordinator):
                         return_value=1)
     mocker.patch.object(coordinator._client, 'ready', return_value=True)
     mocker.patch.object(coordinator._client, 'send')
+    mocker.patch.object(coordinator, '_start_heartbeat_thread')
+    mocker.patch.object(coordinator, '_close_heartbeat_thread')
     mocker.spy(coordinator, '_failed_request')
     mocker.spy(coordinator, '_handle_offset_commit_response')
     mocker.spy(coordinator, '_handle_offset_fetch_response')