Java Reactor StepVerifier.withVirtualTime loop: repeatedly check with "expectNoEvent()", "expectNext()" and "thenAwait()"

Question

I am learning Java 11 reactor. I have seen this example:

    StepVerifier.withVirtualTime(() -> Flux.interval(Duration.ofSeconds(1)).take(3600))
            .expectSubscription()
            .expectNextCount(3600);

This example just checks that with a Flux<Long> which increments 1 after every second till one hour, the final count is 3600.

But, is there any way to check the counter repeatedly after every second?

I know this:

.expectNoEvent(Duration.ofSeconds(1))
.expectNext(0L)
.thenAwait(Duration.ofSeconds(1))

But I have seen no way to repeatedly check this after every second, like:

.expectNoEvent(Duration.ofSeconds(1))
.expectNext(i)
.thenAwait(Duration.ofSeconds(1))

when i increments till 3600. Is there?

---

PS: I tried to add verifyComplete() at last in a long-running tests and it will never end. Do I have to? Or just ignore it?

Answer 1

You can achieve what you wanted by using expectNextSequence. You have to pass an Iterable and include every element you expect to arrive. See my example below:

var longRange = LongStream.range(0, 3600)
    .boxed()
    .collect(Collectors.toList());

StepVerifier
    .withVirtualTime(() -> Flux.interval(Duration.ofSeconds(1)).take(3600))
    .expectSubscription()
    .thenAwait(Duration.ofHours(1))
    .expectNextSequence(longRange)
    .expectComplete().verify();

If you don't add verifyComplete() or expectComplete().verify() then the JUnit test won't wait until elements arrive from the flux and just terminate.

For further reference see the JavaDoc of verify():

this method will block until the stream has been terminated