### Question:
TimerBeepService { public Set<Integer> beep(Timer timer) { this.timerList.add(timer.getId()); this.update(); return this.timerList; }  Set<Integer> beep(Timer timer); Set<Integer> stopBeep(Timer timer);  }### Answer:
@Test public void beepTimerTest() { LocalDateTime timerTime = LocalDateTime.of(2018, 8, 15, 11, 11); Timer timer = new Timer(1, timerTime, null, true); when(this.tbs.beep(timer)).thenReturn(this.timers); this.timers.add(timer.getId()); this.tbs.beep(timer); verify(this.tbs).beep(timer); assertThat(this.tbs.beep(timer).size(), is(1)); }