@Override
    protected boolean validate(Path file) {
      return true;
    }
The cleaner runs in a loop, where it first checks to see all the files under a directory can be
deleted. If they all can, then we try to delete the directory. However, a file may be added
that directory to after the original check. This ensures that we don't accidentally delete that
directory on and don't get spurious IOExceptions.
<p>
This was from HBASE-7465.
@throws Exception on failure
hbase-server/src/test/java/org/apache/hadoop/hbase/master/cleaner/TestCleanerChore.java