protected final ServerName getServerName(Address addr) {
    return TEST_UTIL.getMiniHBaseCluster().getRegionServerThreads().stream()
      .map(t -> t.getRegionServer().getServerName()).filter(sn -> sn.getAddress().equals(addr))
      .findFirst().get();
  }
The server name in group does not contain the start code, this method will find out the start
code and construct the ServerName object.
hbase-server/src/test/java/org/apache/hadoop/hbase/rsgroup/TestRSGroupsBase.java