@Override
    @NonNull
    public Map<ServerName, List<RegionInfo>> retainAssignment(Map<RegionInfo, ServerName> regions,
      List<ServerName> servers) throws HBaseIOException {
      retainAssignCalled = true;
      return super.retainAssignment(regions, servers);
    }
Tests whether the logs are split when master recovers from a expired zookeeper session and an
RS goes down.
hbase-server/src/test/java/org/apache/hadoop/hbase/TestZooKeeper.java