Mocking ScheduledExecutorService.scheduleWithFixedDelay(…) is returning null

问题

In my unit test, I've injected a mocked instance of the ScheduledExecutoryService class into the class that I'm trying to test so that when the scheduleAtFixedRate(...) method is called, it returns a mocked Future. For some reason though, it's always returning null. Any ideas ?

Application code:

Future<?> t = 
scheduledExecutorService.scheduleAtFixedRate(this, 10, 10, TimeUnit.SECONDS);

Test code:

@Mock ScheduledExecutorService scheduledExecutorService;
@Mock ScheduledFuture<?> t;

Mockito.doReturn(t).when(scheduledExecutorService).scheduleWithFixedDelay(
any(Runnable.class), anyLong(), anyLong(), any(TimeUnit.class));

回答1:

You are passing Integers (and probably that is the definition of the method parameters) though you are expecting Long values.

Change to:

Mockito.doReturn(t).when(scheduledExecutorService).scheduleWithFixedDelay(
any(Runnable.class), anyInt(), anyInt(), any(TimeUnit.class));

回答2:

Your application code is using scheduleAtFixedRate, but your test code is only mocking method scheduleWithFixedDelay.

来源：https://stackoverflow.com/questions/43786137/mocking-scheduledexecutorservice-schedulewithfixeddelay-is-returning-null