如何在Angular中对嵌套的订阅方法进行单元测试？

Question

MethodToBeTested() {
  this.serviceA.methodA1().subscribe((response) => {
   if (response.Success) {
     this.serviceA.methodA2().subscribe((res) => {
        this.serviceB.methodB1();
      })
    }
  });
}

Here is the scenario.

Things to test:

1. serviceA.methodA1(). was called.
2. if response.Success then check if serviceA.methodA2() was called
3. check if serviceB.methodB1() was called when serviceA.methodA2() received value.

first, one is easy to test.

let spy = spyOn(serviceA, 'methodA1');
expect(spy).toHaveBeenCalled();

But does one test 2 and 3?

 let spy= spyOn(serviceA, 'methodA1').and.returnValue({subscribe: () => {success:true}});
subject.MethodToBeTested();

something like that?

Answer 1

It would be better to not use a nested subscribe.

Something like this could be a sollution:

let $obs1 = this.serviceA.methodA1().pipe(share());
let $obs2 = $obs1.pipe(switchMap(x => this.serviceA.methodA2()));

$obs1.subsribe(logic1 here...);
$obs2.subsribe(logic2 here...);

Answer 2

Alright, so I figured out what I am looking for is callFake

it('should test inside of subscribe', () => {
    let spy = spyOn(serviceA, 'methodA1').and.callFake(() => {
      return of({ success: true });
    });
    let spy2 = spyOn(serviceA, 'methodA2').and.callFake(() => {
      return of({ success: true });
    });
    let spy3 = spyOn(serviceB, 'methodB1').and.returnValue(of({ success: true }));
     subject.MethodToBeTested();
    expect(spy3).toHaveBeenCalled();
  });

I learned that returnValue won't actually execute the inside of the subscribe while callFake will with the data you provide inside it.