protected static List<ServerName> generateServers(int numServers) {
    List<ServerName> servers = new ArrayList<>(numServers);
    Random rand = ThreadLocalRandom.current();
    for (int i = 0; i < numServers; i++) {
      String host = "server" + rand.nextInt(100000);
      int port = rand.nextInt(60000);
      servers.add(ServerName.valueOf(host, port, -1));
    }
    return servers;
  }
Generate assigned regions to a given server using group information.
@param numRegions the num regions to generate
@param sn         the servername
@return the list of regions
@throws java.io.IOException Signals that an I/O exception has occurred.
hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/RSGroupableBalancerTestBase.java