VirtualTime with Mono.delay hangs in reactor-core:3.7.1

[anuchandy]

The following virtual time test functions correctly with reactor-core:3.4.41, but it hangs with version 3.7.1 (+ and reactor-test:3.7.1). During our upgrade to 3.7.1, we encountered this issue and are currently holding the upgrade. Reporting it in case this points to a potential regression in 3.7.1 itself, could you please take a look?

StepVerifier
    .withVirtualTime(() -> Mono.<Integer>delay(Duration.ofSeconds(5)), () -> VirtualTimeScheduler.create(), 0)
    .thenAwait(Duration.ofSeconds(30))
    .verifyErrorSatisfies(e -> {
    });

Note that with 3.7.1 if I change last argument (n) to 1 then it passes but still need to confirm that if this points to any regression in time related operators (Mono.delay/timeout etc.)

[chemicL]

Hey, @anuchandy!

As far as I understand your test verifies that something has happened but without any request to the upstream (n = 0). Since reactor-core 3.5 the behaviour of Mono has changed in that it is now actually lazy - it only starts processing once it receives a demand, not at subscription time. It is well documented in the release notes and is not a regression in my view. Can you please consult the release notes and let us know whether I properly understood your intent? Thanks.