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A small library for testing time-related stuff
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A small library for testing time-related stuff

Goals and motivation

In a few applications I was struggling with time aspect during tests. It's not hard to write some kind of proxy or mocks to provide a proper date but it is annoying to write them every time. Here comes the idea to create an open source library to help write tests based on the passage of time and also to help write more testable systems.


compile 'io.github.krasnoludkolo:haste:0.2.1'



Haste provides:

  • the implementation of ScheduledExecutorService with advanceTimeBy method to simulate lapse of time.
  • the interface TimeSource to create abstraction over time

Full version

Test scheduled tasks

Some actions in your system may also plan another actions to be done in the future. E.g. when you add a sport fixture you may want to check the result after it has finished When using normal java scheduler it is hard to test results of scheduled jobs without e.g. mocking. Here comes the implementation of ScheduledExecutorService with advanceTimeBy method.

class FooTest{
       private static final Runnable EMPTY_RUNNABLE = () -> {};
       private static final Callable<Integer> RETURN_ONE_CALLABLE = () -> 1;
       void shouldExecuteAllScheduledJobs() throws ExecutionException, InterruptedException {
           BlockingScheduledExecutionService executorService = BlockingScheduledExecutionService.withFixedClockFromNow();
           ScheduledFuture<Integer> schedule1 = executorService.schedule(RETURN_ONE_CALLABLE, 1, TimeUnit.SECONDS);
           ScheduledFuture schedule2 = executorService.schedule(EMPTY_RUNNABLE, 2, TimeUnit.SECONDS);
           ScheduledFuture schedule3 = executorService.schedule(EMPTY_RUNNABLE, 3, TimeUnit.SECONDS);
           ScheduledFuture schedule4 = executorService.schedule(EMPTY_RUNNABLE, 5, TimeUnit.SECONDS);
           executorService.advanceTimeBy(4, TimeUnit.SECONDS);
           assertEquals(Integer.valueOf(1), schedule1.get()); //not null

Get access to current time

With Haste comes the fallowing interface

public interface TimeSource {
    LocalDateTime now();
Standalone time source

If you only need access to current time, without whole ScheduledExecutionService staff, you can use MovableTimeSource with implements TimeSource interface. It simply works like in example

class MovableTimeSourceTest {

    void shouldNowReturnTimeWithOffset() {
        Instant instant = Instant.ofEpochMilli(0);
        ZoneId zoneId = ZoneId.systemDefault();
        Clock clock = Clock.fixed(instant, zoneId);
        MovableTimeSource timeSource = Haste.TimeSource.withFixedClock(clock);

        timeSource.advanceTimeBy(1, TimeUnit.HOURS);

        LocalDateTime now =;

        LocalDateTime expected =;
        assertEquals(expected, now);


ScheduledExecutionService as time source

BlockingScheduledExecutionService from Haste implements that interface so you can obtain 'moved' time like in example

class Event{

    private LocalDateTime eventTime;
    private TimeSource timeSource;

    Event(LocalDateTime eventTime, TimeSource timeSource) {
        if ( {
            throw new IllegalArgumentException("Cannot make event in past");
        this.eventTime = eventTime;
        this.timeSource = timeSource;

    boolean hasAlreadyBegun(){

class EventTest {

    void shouldEventStartsAfterStartDate() {
        BlockingScheduledExecutionService service = BlockingScheduledExecutionService.withFixedClockFromNow();
        LocalDateTime eventTime =;
        Event event = new Event(eventTime, service);
        service.advanceTimeBy(2, TimeUnit.HOURS);


Keep in mind that Haste is in early-alpha phase which means that some API details may change between versions.

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