unit testing a debounce

debouncetest.kt

@Test
fun debounce_test() {
    // TestScheduler lets us control time ;)
    val testScheduler = TestScheduler()

    // This basically represents a button.
    val testClicks = PublishSubject<Long>()

    // This'll let us verify our interactions
    val testSubscriber = TestSubscriber<Long>()

    // Debounce utilizes the computation scheduler by default, so we tell Rx to inject
    // our TestScheduler instead.  This lets us get around having to manually specify some sort
    // of Injectable scheduler in the code, but requires this janky code.
    RxJavaPlugins.getInstance().reset()
    RxJavaPlugins.getInstance().registerSchedulersHook(object : RxJavaSchedulersHook() {
        override fun getComputationScheduler(): Scheduler {
            return testScheduler
        }
    })

    // We want to only accept a click every 100ms
    testClicks.debounce(100, TimeUnit.MILLISECONDS).subscribe(testSubscriber)

    // 3 clicks in quick succession
    testClicks.onNext(1)
    testClicks.onNext(2)
    testClicks.onNext(3)


    // At the start of time, we have no clicks
    testScheduler.triggerActions()
    testSubscriber.assertValueCount(0)

    // After 100 ms, we should have accepted one click
    testScheduler.advanceTimeBy(100, TimeUnit.MILLISECONDS)
    testScheduler.triggerActions()
    testSubscriber.assertValueCount(1)
    testSubscriber.assertValues(3)

    // Emit a few more clicks
    testClicks.onNext(4)
    testClicks.onNext(5)
    testClicks.onNext(6)

    // After 200 ms, we should have accepted two clicks
    testScheduler.advanceTimeBy(100, TimeUnit.MILLISECONDS)
    testScheduler.triggerActions()
    testSubscriber.assertValueCount(2)
    testSubscriber.assertValues(3, 6)
}