@Before
  public void setUp() throws IOException {
    UTIL.getAdmin()
      .createTable(TableDescriptorBuilder.newBuilder(NAME)
        .setColumnFamily(ColumnFamilyDescriptorBuilder.of(CF))
        .setCoprocessor(FlushObserver.class.getName()).build());
    region = UTIL.getHBaseCluster().getRegions(NAME).get(0);
  }
Confirm that the function of FlushLifeCycleTracker is OK as we do not use it in our own code.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestFlushLifeCycleTracker.java