Mocking Time in Spring Boot Tests

Often we need to mock time in when testing logic that is dependent on it. LocalDate, LocalTime, LocalDateTime and ZonedDateTime form the java.time.* package have a method now that accepts an optional clock.  By creating a bean that returns a Clock and inject it into our service using dependency injection we can mock that bean in the tests.

Step 1: Create a ClockBean

Create a configuration class and with a @Bean returning a Clock with the systems current time and zone.

@Configuration
public class ClockConfig {
    @Bean
    Clock clock() {
      return Clock.systemDefaultZone();
    }
}

Step 2: Inject the Clock Bean into your class

Inject the Clock into your logic class using dependency injection. Spring will find the bean you created above. In any calls to LocalDate.now(clock), LocalTime.now(clock), LocalDateTime.now(clock) or ZonedDateTime.now(clock) pass in the injected clock. @Service annotation tells spring to create a singleton bean of this class on the class path.

// Annotate your @Service, @RestController or @Component
@Service
public record MyDateTimeService(Clock clock) { // inject the Clock

    public LocalDateTime currentTime() {
    // Pass the injected clock into the now call.
    return LocalDateTime.now(clock);
    }
}

Step 3: Mock the Clock Bean with any time of your choosing

In the SpringBootTest create a @MockBean Clock and set its time and zone with Mockito. Then call the service you wish to test.

@SpringBootTest
class ShouldIDeployServiceUnitTest {

// Inject the service to test
@Autowired MyDateTimeService serviceUnderTest;

// Mock the Clock Bean
@MockBean Clock clock;

@Test
void setTheClockTo2042() {

    // Set the Mocked Time
    given(clock.instant()).willReturn(Instant.parse("2042-01-01T12:15:00Z"));
    given(clock.getZone()).willReturn(ZoneId.of("UCT"));

    // Call the service
    String actual = serviceUnderTest.currentTime().toString();
    assertThat(actual).isEqualTo("2042-01-01T12:15");
}
}

The same strategy also works for MockMvc integration tests with a standard rest controller.

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.MOCK)
@AutoConfigureMockMvc()
class ShouldIDeployIntegrationTest {
    
    @Autowired
    private MockMvc mockMvc;
    
    @MockBean Clock clock;
    
    @Test
    void setTheClockTo1999() {
    
        given(clock.instant()).willReturn(Instant.parse("1999-09-19T19:19:00Z"));
        given(clock.getZone()).willReturn(ZoneId.of("UCT"));
    
        System.out.println(LocalDateTime.now(clock));
    
        mockMvc.perform(MockMvcRequestBuilders.get("/now"))
            .andExpect(MockMvcResultMatchers.status().isOk())
            .andExpect(MockMvcResultMatchers.content().string("\"1999-09-19T19:19:00\""));
    }
}

Good Luck out there.