public static String formatTimer(long timerInSeconds) {
    final long min = TimeUnit.SECONDS.toMinutes(timerInSeconds);
    final long sec = TimeUnit.SECONDS.toSeconds(timerInSeconds - TimeUnit.MINUTES.toSeconds(min));
    return String.format("%02d:%02d", min, sec);
  }
@Test
  public void testFormatTimer() {
    assertEquals("10:00", formatTimer(600));
    assertEquals("00:00", formatTimer(0));
    assertEquals("00:45", formatTimer(45));
    assertEquals("02:45", formatTimer(165));
    assertEquals("30:33", formatTimer(1833));
  }