Bug/FR: expect(...).toBeObservable(of(...)) should work

[Bielik20]

const value = of('foo');
const expected = of('foo');
expect(value).toBeObservable(expected);

Current Behavior

VSCode informs that Argument of type 'Observable<string>' is not assignable to parameter of type 'ObservableWithSubscriptions' and compilation throws TypeError: Cannot read property 'indexOf' of undefined.

Expected Behavior

Should be able to compare two observables.

Rationale

jasmine-marbles allows this kind of comparisons.

[TheDevelolper]

• 1

[jrista]

This is a severe shortcoming of the jest-marbles library. It does not appear possible to test observables that come from the unit under test given the typing involved in the jest-marbles matchers. Since they must be ObservableWithSubscriptions, which in turn is defined as HotObservable | ColdObservable, it won't match any REAL observable...

The jasmine-marbles matchers type the toBeObservable matcher as simply any.