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Question

We are using rx-java, but we have a problem to test if an Observable is evaluated only once.

We have the following signature of services:

class A {
  Observable<String> computeA();
}

class B {
  Observable<Void> computeB(String inputA)
}

class C {
  Observable<Void> computeC(String inputA)
}

In our case we have a service that invokes a service A, and we use the result of this service as input to another two service B and C. We want to check that the service A in only invoked once.

We tried to do it using AtomicInteger as a counter mocking the Observable of service A or just mocking Observable.OnSubscribe checking the times call is invoked, but the test turns very difficult to read.

The question is: Is there any cleaner way to do this kind of test?

Answer 1

We usually do this by adding an

source
.doOnSubscribe(() -> counter.getAndIncrement())
.op()
.op()
...

at the required place and check the counter value after things quiet down.

Note that we have an operator called publish() that makes sure a source is subscribed to once and all side-effects of it happen only once (as long as connect() is called once).