it('should get Date diff correctly in fakeAsync with rxjs scheduler', fakeAsync(() => {
     // need to add `import 'zone.js/dist/zone-patch-rxjs-fake-async'
     // to patch rxjs scheduler
     let result = null;
     of ('hello').pipe(delay(1000)).subscribe(v => { result = v; });
     expect(result).toBeNull();
     tick(1000);
     expect(result).toBe('hello');
 
     const start = new Date().getTime();
     let dateDiff = 0;
     interval(1000).pipe(take(2)).subscribe(() => dateDiff = (new Date().getTime() - start));
 
     tick(1000);
     expect(dateDiff).toBe(1000);
     tick(1000);
     expect(dateDiff).toBe(2000);
   }));