@Override
      public boolean evaluate() throws Exception {
        for (RegionServerThread thread : UTIL.getHBaseCluster().getRegionServerThreads()) {
          HRegionServer rs = thread.getRegionServer();
          if (rs != rsToSuspend) {
            return !rs.getRegions(TABLE_NAME).isEmpty();
          }
        }
        return false;
      }
This testcase is used to ensure that the compaction marker will fail a compaction if the RS is
already dead. It can not eliminate FNFE when scanning but it does reduce the possibility a lot.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestCompactionInDeadRegionServer.java