@Override
      public void handleDataChange(String dataPath, Object data) throws Exception { }
electionLatch and count together verify that:
1. the registered listeners are actually invoked by the ZkClient on the correct path
2. for a single participant failure, at-most 1 other participant is notified
samza-core/src/test/java/org/apache/samza/zk/TestZkLeaderElector.java