@Test
  public void testDeleteCallback() {
    scheduler.deleteCallback("string_key");
    verify(epochTimeScheduler).deleteTimer("string_key");

    // check some other type of key
    scheduler.deleteCallback(777);
    verify(epochTimeScheduler).deleteTimer(777);
  }
deleteCallback should delegate to the inner scheduler
samza-core/src/test/java/org/apache/samza/scheduler/TestCallbackSchedulerImpl.java