How to perform assertion on all remaining elements in StepVerifier?

Question

StepVerifier has an assertNext method that allows performing an assertion on a value of next element.

    StepVerifier.create(dataFlux)
            .assertNext(v -> checkValue(v)
            .verifyComplete();

What is a good way to perform assertion for every remaining element (e.g. to check that every element is positive)? I'd expect something like assertEveryNextElement method.

Answer 1

My first attempt to perform assertion on all elements of a flux was

StepVerifier.create(dataFlux)
        .recordWith(ArrayList::new)
        .thenConsumeWhile(x -> true)  // Predicate on elements
        .consumeRecordedWith(matches ->
            matches.forEach(v -> checkValue(v)))
        .verifyComplete();

UPD Simon Baslé suggested to use just thenConsumeWhile, it rethrows AssertionErrors.

StepVerifier.create(dataFlux)
        .thenConsumeWhile(v -> {
            assertThat(v).equalsTo(expected);
            return true;
        })
        .verifyComplete();

And more canonical way to use StepVerifier for this task would be:

StepVerifier.create(dataFlux)
        .thenConsumeWhile(v -> return expected.equals(v))
        .verifyComplete();

Answer 2

The expected way to do that is to actually use the thenConsumeWhile operator and provide a predicate. If there is any element in the sequence that doesn't match, the StepVerifier will error.

It is not assertion-based though, taking a Predicate rather than a Consumer. That said you could still use an assertion library, any AssertionError should fail the test (you still have to return a bogus predicate result).

(side warning: keep in mind this doesn't work well with infinite sequences)