How do I use Reactor's StepVerifier to verify a Mono is empty?

Question

I am using StepVerifier to test values:

@Test
public void testStuff() {
    Thing thing = new Thing();
    Mono<Thing> result = Mono.just(thing);
    StepVerifier.create(result).consumeNextWith(r -> {
        assertEquals(thing, r);
    }).verifyComplete();
}

What I'd like to do now is test for the absence of an item in the Mono. Like this:

@Test
public void testNoStuff() {
    Mono<Thing> result = Mono.empty();
    StepVerifier.create(result)... // what goes here?
}

I want to test that the Mono is in fact empty. How do I do that?

score 84 · Accepted Answer · answered Jul 23 '18 at 13:01

84

Simply use verifyComplete(). If the Mono emits any data, it will fail the stepverifier as it doesn't expect an onNext signal at this point.

answered Jul 23 '18 at 13:01

Simon Baslé

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samibel · Answer 2 · 2020-12-23T14:33:16.970

18

here it is checked that onNext is not called

 StepVerifier.create(result).expectNextCount(0).verifyComplete()

edited Dec 23 '20 at 14:33

answered Dec 07 '20 at 15:48

samibel

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Please explain the difference to the other, older, upvoted answer. It seems that you recommend the same thing, just without any explanation – Yunnosch Dec 07 '20 at 23:05

How do I use Reactor's StepVerifier to verify a Mono is empty?

2 Answers2