Test Typescript Service : Multiple Subscription on one Observable

Question

I am having a problem performing a test on a typescript service. I have a function that returns an observable. I use .subscribe() to look at the result and verify assertions. When I do a test with a single .subscribe() on this observable everything works fine. But when I add another call to .subscribe() to my test after changing some variables or not I get inconsistent results for my whole test. For example, the entire test is successful while some assertions are false Could you help me understand where the problem comes from please? I still have troubles with observables..

public myFunction(param1: string, param2: string): Observable<boolean> {
  return this.apiService.apiName(param1, param2)
    .pipe(
      map(response => {
        return boolean depending on the response
      }),
      catchError((err) => {
        return throwError(err);
      })
    );
}

Test OK because it returns an error :

it('test', (done) => {

  apiService.apiName.andCallFake(() => of(response));

  spectator.service.myFonction('param1', 'param2')
    .subscribe(
      (res) => {
        expect(res).toEqual(false); // should return an error because res = true
        done();
      },
      () => fail()
    );

}

Test KO because it doesn't return an error:

it('test', (done) => {
  apiService.apiName.andCallFake(() => of(response));

  spectator.service.myFunction('param1', 'param2')
    .subscribe(
      (res) => {
        expect(res).toEqual(false); // should return an error because res = true
        done();
      },
      () => fail()
    );
  
  --Modification of variables or not--

  spectator.service.myFunction('param1', 'param2')
    .subscribe(
      (res) => {
        expect(res).toEqual(true); // should not return an error because res = true
        done();
      },
      () => fail()
    );

}