Testing mock with Clock object for LocalDateTime now

 LocalDateTime.now() will create problem when unit testing, for this purpose using help of Clock object is recommended way.

Let's see example:

@Service
@RequiredArgsConstructor
@Slf4j
public class OrdersServiceImpl implements OrdersService {

    private final OrdersRepository ordersRepository;
    private final OrdersDeliveryEventsRepository ordersDeliveryEventsRepository;
    private final MailService mailService;
    private final Clock clock = Clock.systemDefaultZone();
    private final FileGenerator fileGenerator;

    @Override
    @Scheduled(cron = "${cron.expression}")
    @SchedulerLock(name = "TaskScheduler_processOrders",
            lockAtMostFor = "15M", lockAtLeastFor = "2M")
    public void processOrders() throws IOException {
        log.info("processOrders started");
        List<OrdersEntity> unsentOrders = ordersRepository
                .getUnsentOrders(LocalDateTime.now(clock).minusDays(7), LocalDateTime.now(clock));
        if (unsentOrders.isEmpty()) {
            log.warn("There are not any orders for now");
            return;
        }

Firstly we create Clock object with sysemdefaultZone and then pass this

argument to LocalDateTime.now(clock) in service class; 

Testing for this:

We have to mock Clock.systemDefaultZone(); that is static method calling

via directly mentioned class,

but Mockito static methods mocking

way is different from non/static ones.

Firstly we have to add 2 dependencies:

testCompile group: 'org.mockito', name: 'mockito-inline',version: '3.6.0'
testCompile group: 'org.mockito', name: 'mockito-core', version: '4.3.1'
in our test method will be in this form:

@ExtendWith(MockitoExtension.class)
class OrdersServiceImplTest {

    static Clock clock;
    private static MockedStatic<Clock> mockedClock;
    @Mock
    private OrdersRepository ordersRepository;
    @Mock
    private OrdersDeliveryEventsRepository ordersDeliveryEventsRepository;
    @Mock
    private MailService mailService;

    @Mock
    private FileGenerator fileGenerator;

    @InjectMocks
    private OrdersServiceImpl ordersService;

    @BeforeAll
    static void setupClock() {
        LocalDateTime localdatetime =
                LocalDateTime.of(2022, 6, 7, 16, 4, 5);
        clock = Clock.fixed(localdatetime.atZone(ZoneId.systemDefault()).toInstant(),
                ZoneId.systemDefault());

        mockedClock = mockStatic(Clock.class);
        mockedClock.when(Clock::systemDefaultZone).thenReturn(clock);
    }

    @AfterAll
    static void close() {
        mockedClock.close();
    }

    @Test
    void processOrders() throws IOException {
        var ordersEntity = new OrdersEntity();
        ordersEntity.setId(1L);
        ordersEntity.setFullName("Test Testov");
        ordersEntity.setEmail("test@test.com");

        var mailResponse = new MailResponse();
        mailResponse.setStatus(DeliveryStatus.SENT);
        mailResponse.setMail(new MailContent());

        when(ordersRepository.getUnsentOrders(LocalDateTime.now(clock).minusDays(7),
                LocalDateTime.now(clock)));
}
}

Setup clock with MockedStatic object is necessary and after all tests

executed we must close this object, otherwise it will occupy

the current thread and we cann't create again same of this object in other

classes.