JUnit with Java 8 Clock

Question

Imagine we have the following class that I would like to test:

class Times {

    Clock cl = Clock.systemDefaultZone();

    public int changeTime() {
        LocalDate ld = LocalDate.now(cl);
        if(ld.getMonth().equals(Month.OCTOBER))
            return 1;
        if(ld.getMonth().equals(Month.NOVEMBER))
            return 2;
        return 0;
    }
}

How can I force the date to be in November and assert that the method returns 2?

I am using JUnit and Mockito.

Answer 1

Assuming there is a setter for the Clock object in Times class, you can do something like this:

Times times = new Times();
Clock fixedClockInNovember = Clock.fixed(Instant.parse("2015-11-01T00:00:00.00Z"), ZoneId.of("UTC"));
times.setClock(fixedClockInNovember);
assertEquals(2, times.changeTime());

In this code, a fixed clock is created. This simulates a constant time for the given instant, that is in November.

As such, any call to LocalDate.now(clock) will always return the same date in November.