How to test Nothing Happens Until You subscribe() - project-reactor

Question

return Mono.just(key) //
.map(Service1::doSomething) //
.map(Service2:: doSomething) //
.map(Service3::getBytes);
My code is as above, I have many logs in the methods of services (Service1, Service2 and Service3), so I can confirm that those methods are not called, till I call subscribe method by manually verifying the log files. Are there any testing tools which can help me automate that testing?

Answer 1

Mokito can track invocations using mocks/spys. Here's an example using Spring:
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.mock.mockito.SpyBean;
import org.springframework.test.context.junit4.SpringRunner;
import reactor.core.publisher.Mono;
import reactor.test.StepVerifier;
#RunWith(SpringRunner.class)
public class ExampleTests {
#SpyBean
private Service1 service1;
#SpyBean
private Service2 service2;
#SpyBean
private Service3 service3;
#Test
public void verifyNothingHappensWithoutSubscribe() {
Mono.just("key")
.map(service1::doSomething)
.map(service2::doSomething)
.map(service3::getBytes);
verify(service1, times(0)).doSomething("key");
verify(service2, times(0)).doSomething("key");
verify(service3, times(0)).getBytes("key");
}
#Test
public void verifyCallsWhenSubscribed() {
Mono<byte[]> testMono = Mono.just("key")
.map(service1::doSomething)
.map(service2::doSomething)
.map(service3::getBytes);
StepVerifier.create(testMono)
.expectNextCount(1)
.verifyComplete();
verify(service1, times(1)).doSomething("key");
verify(service2, times(1)).doSomething("key");
verify(service3, times(1)).getBytes("key");
}
}