如何对 rxjs shareReplay 进行单元测试？

Question

I am trying to test the following scenario for a service using RxJS's shareReplay method which caches the response so that subsequent subscriptions do not need to make another call:

it('should only make 1 http call for multiple subscriptions', () => {

  myService.doSomeAsyncOperation('ABCD').subscribe();
  myService.doSomeAsyncOperation('EFGH').subscribe();
  myService.doSomeAsyncOperation('IJKL').subscribe();

  // Expectation?

});

It would seem that exposing some form of observable state is necessary to test this properly, eg .getCallsMade() which could be used to say:

expect(myService.doSomeAsyncOperation('IJKL').subscribe().getHttpCallsMade() < 2).toBeTruthy()

I could add a counter and try to do this manually, but this doesn't seem optimal as it's quite a bit of state to manage.

Any ideas?

Answer 1

Seems this is the answer:

httpTestingController.expectOne('endpoint-called-from-async-operation');

https://angular.io/api/common/http/testing/HttpTestingController#expectone