public static String durationToString(long durationMs) {
    return DFSUtilClient.durationToString(durationMs);
  }
@Test(timeout=10000)
  public void testDurationToString() throws Exception {
    assertEquals("000:00:00:00.000", DFSUtil.durationToString(0));
    assertEquals("001:01:01:01.000",
        DFSUtil.durationToString(((24*60*60)+(60*60)+(60)+1)*1000));
    assertEquals("000:23:59:59.999",
        DFSUtil.durationToString(((23*60*60)+(59*60)+(59))*1000+999));
    assertEquals("-001:01:01:01.000",
        DFSUtil.durationToString(-((24*60*60)+(60*60)+(60)+1)*1000));
    assertEquals("-000:23:59:59.574",
        DFSUtil.durationToString(-(((23*60*60)+(59*60)+(59))*1000+574)));
  }