Mocking time in Java 8's java.time API

Question

Joda Time has a nice DateTimeUtils.setCurrentMillisFixed() to mock time.

It\'s very practical in tests.

Is there an equivalent in Java 8\'s java.time API

Answer 1

This example even shows how to combine Instant and LocalTime (detailed explanation of issues with the conversion)

A class under test

import java.time.Clock;
import java.time.LocalTime;

public class TimeMachine {

    private LocalTime from = LocalTime.MIDNIGHT;

    private LocalTime until = LocalTime.of(6, 0);

    private Clock clock = Clock.systemDefaultZone();

    public boolean isInInterval() {

        LocalTime now = LocalTime.now(clock);

        return now.isAfter(from) && now.isBefore(until);
    }

}

A Groovy test

import org.junit.Test
import org.junit.runner.RunWith
import org.junit.runners.Parameterized

import java.time.Clock
import java.time.Instant

import static java.time.ZoneOffset.UTC
import static org.junit.runners.Parameterized.Parameters

@RunWith(Parameterized)
class TimeMachineTest {

    @Parameters(name = "{0} - {2}")
    static data() {
        [
            ["01:22:00", true,  "in interval"],
            ["23:59:59", false, "before"],
            ["06:01:00", false, "after"],
        ]*.toArray()
    }

    String time
    boolean expected

    TimeMachineTest(String time, boolean expected, String testName) {
        this.time = time
        this.expected = expected
    }

    @Test
    void test() {
        TimeMachine timeMachine = new TimeMachine()
        timeMachine.clock = Clock.fixed(Instant.parse("2010-01-01T${time}Z"), UTC)
        def result = timeMachine.isInInterval()
        assert result == expected
    }

}

Answer 2

I need LocalDate instance instead of LocalDateTime.
With such reason I created following utility class:

public final class Clock {
    private static long time;

    private Clock() {
    }

    public static void setCurrentDate(LocalDate date) {
        Clock.time = date.toEpochDay();
    }

    public static LocalDate getCurrentDate() {
        return LocalDate.ofEpochDay(getDateMillis());
    }

    public static void resetDate() {
        Clock.time = 0;
    }

    private static long getDateMillis() {
        return (time == 0 ? LocalDate.now().toEpochDay() : time);
    }
}

And usage for it is like:

class ClockDemo {
    public static void main(String[] args) {
        System.out.println(Clock.getCurrentDate());

        Clock.setCurrentDate(LocalDate.of(1998, 12, 12));
        System.out.println(Clock.getCurrentDate());

        Clock.resetDate();
        System.out.println(Clock.getCurrentDate());
    }
}

Output:

2019-01-03
1998-12-12
2019-01-03

Replaced all creation LocalDate.now() to Clock.getCurrentDate() in project.

Because it is spring boot application. Before test profile execution just set a predefined date for all tests:

public class TestProfileConfigurer implements ApplicationListener<ApplicationPreparedEvent> {
    private static final LocalDate TEST_DATE_MOCK = LocalDate.of(...);

    @Override
    public void onApplicationEvent(ApplicationPreparedEvent event) {
        ConfigurableEnvironment environment = event.getApplicationContext().getEnvironment();
        if (environment.acceptsProfiles(Profiles.of("test"))) {
            Clock.setCurrentDate(TEST_DATE_MOCK);
        }
    }
}

And add to spring.factories:

org.springframework.context.ApplicationListener=com.init.TestProfileConfigurer

Answer 3

I used a field

private Clock clock;

and then

LocalDate.now(clock);

in my production code. Then I used Mockito in my unit tests to mock the Clock using Clock.fixed():

@Mock
private Clock clock;
private Clock fixedClock;

Mocking:

fixedClock = Clock.fixed(Instant.now(), ZoneId.systemDefault());
doReturn(fixedClock.instant()).when(clock).instant();
doReturn(fixedClock.getZone()).when(clock).getZone();

Assertion:

assertThat(expectedLocalDateTime, is(LocalDate.now(fixedClock)));

Answer 4

I find using Clock clutters your production code.

You can use JMockit or PowerMock to mock static method invocations in your test code. Example with JMockit:

@Test
public void testSth() {
  LocalDate today = LocalDate.of(2000, 6, 1);

  new Expectations(LocalDate.class) {{
      LocalDate.now(); result = today;
  }};

  Assert.assertEquals(LocalDate.now(), today);
}

EDIT: After reading the comments on Jon Skeet's answer to a similar question here on SO I disagree with my past self. More than anything else the argument convinced me that you cannot parallize tests when you mock static methods.

You can/must still use static mocking if you have to deal with legacy code, though.

Answer 5

Here's a working way to override current system time to a specific date for JUnit testing purposes in a Java 8 web application with EasyMock

Joda Time is sure nice (thank you Stephen, Brian, you've made our world a better place) but I wasn't allowed to use it.

After some experimenting, I eventually came up with a way to mock time to a specific date in Java 8's java.time API with EasyMock

• Without Joda Time API
• Without PowerMock.

Here's what needs to be done:

What needs to be done in the tested class

Step 1

Add a new java.time.Clock attribute to the tested class MyService and make sure the new attribute will be initialized properly at default values with an instantiation block or a constructor:

import java.time.Clock;
import java.time.LocalDateTime;

public class MyService {
  // (...)
  private Clock clock;
  public Clock getClock() { return clock; }
  public void setClock(Clock newClock) { clock = newClock; }

  public void initDefaultClock() {
    setClock(
      Clock.system(
        Clock.systemDefaultZone().getZone() 
        // You can just as well use
        // java.util.TimeZone.getDefault().toZoneId() instead
      )
    );
  }
  { initDefaultClock(); } // initialisation in an instantiation block, but 
                          // it can be done in a constructor just as well
  // (...)
}

Step 2

Inject the new attribute clock into the method which calls for a current date-time. For instance, in my case I had to perform a check of whether a date stored in database happened before LocalDateTime.now(), which I replaced with LocalDateTime.now(clock), like so:

import java.time.Clock;
import java.time.LocalDateTime;

public class MyService {
  // (...)
  protected void doExecute() {
    LocalDateTime dateToBeCompared = someLogic.whichReturns().aDate().fromDB();
    while (dateToBeCompared.isBefore(LocalDateTime.now(clock))) {
      someOtherLogic();
    }
  }
  // (...) 
}

What needs to be done in the test class

Step 3

In the test class, create a mock clock object and inject it into the tested class's instance just before you call the tested method doExecute(), then reset it back right afterwards, like so:

import java.time.Clock;
import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import org.junit.Test;

public class MyServiceTest {
  // (...)
  private int year = 2017;  // Be this a specific 
  private int month = 2;    // date we need 
  private int day = 3;      // to simulate.

  @Test
  public void doExecuteTest() throws Exception {
    // (...) EasyMock stuff like mock(..), expect(..), replay(..) and whatnot
 
    MyService myService = new MyService();
    Clock mockClock =
      Clock.fixed(
        LocalDateTime.of(year, month, day, 0, 0).toInstant(OffsetDateTime.now().getOffset()),
        Clock.systemDefaultZone().getZone() // or java.util.TimeZone.getDefault().toZoneId()
      );
    myService.setClock(mockClock); // set it before calling the tested method
 
    myService.doExecute(); // calling tested method 

    myService.initDefaultClock(); // reset the clock to default right afterwards with our own previously created method

    // (...) remaining EasyMock stuff: verify(..) and assertEquals(..)
    }
  }

Check it in debug mode and you will see the date of 2017 Feb 3 has been correctly injected into myService instance and used in the comparison instruction, and then has been properly reset to current date with initDefaultClock().

Answer 6

With the help of PowerMockito for a spring boot test you can mock the ZonedDateTime. You need the following.

Annotations

On the test class you need to prepare the service which uses the the ZonedDateTime.

@RunWith(PowerMockRunner.class)
@PowerMockRunnerDelegate(SpringRunner.class)
@PrepareForTest({EscalationService.class})
@SpringBootTest
public class TestEscalationCases {
  @Autowired
  private EscalationService escalationService;
  //...
}

Test case

In the test you can prepare a desired time, and get it in response of the method call.

  @Test
  public void escalateOnMondayAt14() throws Exception {
    ZonedDateTime preparedTime = ZonedDateTime.now();
    preparedTime = preparedTime.with(DayOfWeek.MONDAY);
    preparedTime = preparedTime.withHour(14);
    PowerMockito.mockStatic(ZonedDateTime.class);
    PowerMockito.when(ZonedDateTime.now(ArgumentMatchers.any(ZoneId.class))).thenReturn(preparedTime);
    // ... Assertions 
}