  @Test
  public void testScheduleCallback() {

    @SuppressWarnings("unchecked")
    ScheduledCallback<String> stringCallback = mock(ScheduledCallback.class);
    scheduler.scheduleCallback("string_key", 123, stringCallback);
    verify(epochTimeScheduler).setTimer("string_key", 123, stringCallback);

    // check some other type of key
    @SuppressWarnings("unchecked")
    ScheduledCallback<Integer> intCallback = mock(ScheduledCallback.class);
    scheduler.scheduleCallback(777, 456, intCallback);
    verify(epochTimeScheduler).setTimer(777, 456, intCallback);
  }