@BeforeClass
  public static void setUp() {
    POOL = DirScanPool.getHFileCleanerScanPool(TEST_UTIL.getConfiguration());
  }
Test the HFileLink Cleaner. HFiles with links cannot be deleted until a link is present.
hbase-server/src/test/java/org/apache/hadoop/hbase/master/cleaner/TestHFileLinkCleaner.java