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

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 {
    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