Unit testing retries with project reactor - unit-testing

Question

I have a piece of code that goes something like this:
somePublisher
.subscribeOn(...)
.flatMap { x -> someFunctionThatReturnsMono(x) }
.retry(3)
.subscribe()
So far I have managed to unit test happy paths, like whether the code inside map {...} is getting called, using the tools from reactor-test.
Now I want to test errors and retries. How can I test to make sure someFunctionThatReturnsMono(x) is getting called at most 4 times when consecutive errors occur?

Answer 1

Simple way is to mock function and count its calls:
def 'Test retry'(){
setup:
someBean = Mock(SomeBean)
def testMono = Mono.just(X)
.flatMap { x -> someBean.someFunctionThatReturnsMono(x) }
.retry(3)
.subscribeOn(Schedulers.elastic())
when:
StepVerifier.create(testMono).verifyError(IllegalArgumentException)
then:
4 * someBean.someFunctionThatReturnsMono(_ as X) >> Mono.error(new IllegalArgumentException())
}
Another one is to mock funtion to return PublisherProbe and count probe subscriptions:
def 'Test retry'() {
when:
PublisherProbe probe = PublisherProbe.of(Mono.error(new IllegalArgumentException()))
someBean = Mock(SomeBean) {
someFunctionThatReturnsMono(_) >> probe
}
def testMono = Mono.just(X)
.flatMap { x -> someBean.someFunctionThatReturnsMono(x) }
.retry(3)
.subscribeOn(Schedulers.elastic())
then:
StepVerifier.create(testMono).verifyError(IllegalArgumentException)
probe.subscribeCount() == 4
}

Answer 2

This is how I do it for one of my use-cases:
def "should retry failed action given number of times"() {
given:
def invocationCounter = new AtomicInteger(0)
when:
Mono<Void> mono = myService.doSth()
.doOnError { invocationCounter.incrementAndGet() }
then:
StepVerifier.create(mono)
.verifyErrorMatches { it == expectedError }
and:
invocationCounter.get() == 1 + retryNum
}