cluster2.killOneBackupZooKeeperServer();
assertEquals(0, cluster2.getBackupZooKeeperServerNum());
assertEquals(1, cluster2.getZooKeeperServerNum());
// killing the last zk server
currentActivePort = cluster2.killCurrentActiveZooKeeperServer();
assertTrue(currentActivePort == -1);
assertTrue(cluster2.getClientPort() == currentActivePort);
// this should do nothing.
cluster2.killOneBackupZooKeeperServer();
assertEquals(-1, cluster2.getBackupZooKeeperServerNum());