@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);
  }
scheduleCallback should delegate to the inner scheduler
samza-core/src/test/java/org/apache/samza/scheduler/TestCallbackSchedulerImpl.java