static WALFactory createWALFactory(Configuration conf, Path rootDir) throws IOException {
    Configuration confForWAL = new Configuration(conf);
    confForWAL.set(HConstants.HBASE_DIR, rootDir.toString());
    return new WALFactory(confForWAL, "hregion-" + RandomStringUtils.randomNumeric(8));
  }
For this test,the spied {@link AsyncFSWAL} can not work properly because of a Mockito defect
that can not deal with classes which have a field of an inner class. See discussions in
HBASE-15536.When we reuse the code of {@link AsyncFSWAL} for {@link FSHLog}, this test could
not work for {@link FSHLog} also.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestHRegion.java