WIP: add test sample with zone-testing

[JiaLiPassion]

Description:

This PR is based on @benlesh 's document here. https://docs.google.com/document/d/1sIUgRVRgcsLcC8B5sbCAPDvA_lrYcACzh9Q80vxFTbw/

This is a experimental PR to try to let rxjs test with zone-testing, this PR will use the experimental version of zone.js (angular/zone.js#1084) . So with adding more test cases, we will find more use cases and find out current zone-testing APIs satisfy the rxjs requirements or not.

Current status:

1. add zone-testing fakeAsync test cases for combineLatest, use setInterval to create Observable, those async test cases was originally handled by TestScheduler.

function createIntervalObservable(interval: number) {
  return new Observable<number>(subscriber => {
    let i = 0;
    const id = setInterval(() => {
      subscriber.next(i++);
    }, interval);
    return () => clearInterval(id);
  });
}

it('should combine the latest values of multiple observables with fakeAsync', fakeAsyncTest(() => {
    const results: any[] = [];
    const s1 = createIntervalObservable(1000);
    const s2 = createIntervalObservable(1500);
    const s3 = createIntervalObservable(1800);
    combineLatest(s1, s2, s3).subscribe({
      next(value) { results.push(value); },
      complete() { results.push('done'); },
    });
    expect(results).toEqual([]);
    tick(1000);
    expect(results).toEqual([]);
    tick(500);
    expect(results).toEqual([]);
    tick(300);
    expect(results).toEqual([[0, 0, 0]]);
    tick(300);
    expect(results).toEqual([[0, 0, 0], [1, 0, 0]]);
    clearAllMacrotasks();
  }));

2. TODO: try to add marble test sample with zone-testing later.

Related issue (if exists):

[benlesh]

This is awesome! Thanks, @JiaLiPassion! I'm going to take this example and try to work out what the next generation of marble testing looks like. We're likely to have to change a few things to accommodate the fact that async/await cannot be hooked ala zones.

[benlesh]

(Marked as "blocked", because I'm not sure I'll merge this straight in, or just use it as an example.)

[JiaLiPassion]

@benlesh, thanks, I just use this PR as a discussion place, so we can discuss whether zone-testing can satisfy rxjs requirement or not.

We're likely to have to change a few things to accommodate the fact that async/await cannot be hooked ala zones.

in nodejs with asynchooks, we can hooks with zone, here I created a POC PR, angular/zone.js#795
But in browser, it will not work...

[benlesh]

@JiaLiPassion ... I'm closing this, but only to unclutter the pulls list. This is definitely going to be used as a reference for future work on the test scheduler, which there is still ongoing design work for.

[JiaLiPassion]

@benlesh, sure, if there is anything need to do in zone-testing, please let me know.