How to unit test nested subscribe methods in Angular?

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:

serviceA.methodA1(). was called.
if response.Success then check if serviceA.methodA2() was called
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?

SamuraiJack · Accepted Answer · 2019-07-09 07:41:29Z

3

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.

answered Jul 9, 2019 at 7:41

SamuraiJack

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Comments

Robin Dijkhof · Accepted Answer · 2019-07-08 18:34:25Z

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...);

answered Jul 8, 2019 at 18:34

Robin Dijkhof

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1 Comment

SamuraiJack Over a year ago

Let's say, it's somebody else's existing code. And I can't change the code. But I have to write tests.

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