@Override
    public void run() {
      manager.blockUntilBecomingActiveMaster(100, mockTaskGroup());
      LOG.info("Second master has become the active master!");
      isActiveMaster = true;
    }
Assert there is an active master and that it has the specified address.
@param zk              single Zookeeper watcher
@param expectedAddress the expected address of the master
@throws KeeperException unexpected Zookeeper exception
@throws IOException     if an IO problem is encountered
hbase-server/src/test/java/org/apache/hadoop/hbase/master/TestActiveMasterManager.java