@Test
    fun a() {
        val ts = TestScheduler()
        val ps = PublishSubject.create<Int>()
        val s = TestSubscriber.create<Int>()
        val threshold = 3

        ps.switchMap { value ->
            when {
                value > threshold -> Observable.timer(3, SECONDS, ts).map { value }
                else -> Observable.never()
            }
        }.subscribe(s)

        ps.onNext(1)
        ts.advanceTimeBy(5, SECONDS)

        ps.onNext(2)
        ts.advanceTimeBy(5, SECONDS)

        ps.onNext(3)
        ts.advanceTimeBy(2, SECONDS)

        ps.onNext(4)
        ts.advanceTimeBy(4, SECONDS)

        ps.onNext(5)
        ts.advanceTimeBy(4, SECONDS)

        s.assertValues(4, 5)
    }