How can I mock java.time.LocalDate.now()

Question

In my test case, I need test time sensitive method, in that method we're using java 8 class LocalDate, it is not Joda.

What can I do to change time, when I'm running test

Answer 1

You might also want to pass a fixed clock in production (the value of which is fixed at the start of a transaction) to avoid using inconsistent "now" in different entities and requests. See this question for details.

Answer 2

In your code, replace LocalDate.now() with LocalDate.now(clock);.

You can then pass Clock.systemDefaultZone() for production and a fixed clock for testing.

Answer 3

You can refactor you code to make it test-friendly, for example, replace all invocations of LocalDate.now() with invocation of some method of custom mockable non-static class.

Alternatively, you can use PowerMock's mockStatic.

Answer 4

If we need to mock static methods like now() we can use multiple alternatives like PowerMock:

@RunWith(PowerMockRunner.class)
@PrepareForTest({ LocalDateTime.class })
public class LocalDateTimeUnitTest {

    @Test
    public void givenLocalDateTimeMock_whenNow_thenGetFixedLocalDateTime() {
        Clock clock = Clock.fixed(Instant.parse("2014-12-22T10:15:30.00Z"), ZoneId.of("UTC"));
        LocalDateTime dateTime = LocalDateTime.now(clock);
        mockStatic(LocalDateTime.class);
        when(LocalDateTime.now()).thenReturn(dateTime);
        String dateTimeExpected = "2014-12-22T10:15:30";

        LocalDateTime now = LocalDateTime.now();

        assertThat(now).isEqualTo(dateTimeExpected);
    }
}

Or JMockit, indeed with JMockit we can use the MockUp class:

@Test
public void givenLocalDateTimeWithJMock_whenNow_thenGetFixedLocalDateTime() {
    Clock clock = Clock.fixed(Instant.parse("2014-12-21T10:15:30.00Z"), ZoneId.of("UTC"));
    new MockUp<LocalDateTime>() {
        @Mock
        public LocalDateTime now() {
            return LocalDateTime.now(clock);
        }
    };
    String dateTimeExpected = "2014-12-21T10:15:30";

    LocalDateTime now = LocalDateTime.now();

    assertThat(now).isEqualTo(dateTimeExpected);
}

Or the Expectations class:

@Test
public void givenLocalDateTimeWithExpectations_whenNow_thenGetFixedLocalDateTime() {
    Clock clock = Clock.fixed(Instant.parse("2014-12-23T10:15:30.00Z"), ZoneId.of("UTC"));
    LocalDateTime dateTimeExpected = LocalDateTime.now(clock);
    new Expectations(LocalDateTime.class) {
        {
            LocalDateTime.now();
            result = dateTimeExpected;
        }
    };

    LocalDateTime now = LocalDateTime.now();

    assertThat(now).isEqualTo(dateTimeExpected);
}

We can find more examples here.

Another simple alternative is to use the now() method with a fixed Clock instance. Certainly, most of the classes in java.time package have a now() method with a Clock parameter:

@Test
public void givenFixedClock_whenNow_thenGetFixedLocalDateTime() {
    Clock clock = Clock.fixed(Instant.parse("2014-12-22T10:15:30.00Z"), ZoneId.of("UTC"));
    String dateTimeExpected = "2014-12-22T10:15:30";

    LocalDateTime dateTime = LocalDateTime.now(clock);

    assertThat(dateTime).isEqualTo(dateTimeExpected);
}