it('should support a scheduler', () => {
  const o = of('a', 'b', 'c').pipe(timeout(10, asyncScheduler)); // $ExpectType Observable<string>
  const p = of('a', 'b', 'c').pipe(timeout(new Date(), asyncScheduler)); // $ExpectType Observable<string>
});

 concatMap(() => options.deleteOutputPath
   ? this._deleteOutputDir(root, normalize(options.outputPath), this.context.host)
   : of(null)),

it('should enforce types', () => {
  const o = of('a', 'b', 'c').pipe(repeat('aa')); // $ExpectError
});

it('should support an undefined predicate with a T default', () => {
  const o = of('foo').pipe(last(undefined, 'bar')); // $ExpectType Observable<string>
});

 mergeMap((x: string) => of(x))

 // getHeroes(): Hero[]{
 //   return HEROES
 // }
 getHeroes(): Observable<Hero[]> {
   // return of(HEROES);
   this.messageService.add('HeroService:    xxxx');
   return of(HEROES)
 }

 getSystem(): Observable<DotWorkflow> {
     const systemWorkflow = mockWorkflows.filter((workflow: DotWorkflow) => workflow.system);
     return observableOf(_.cloneDeep(systemWorkflow[0]));
 }

      factory: () => (fem: Tree) => {
        inner = fem;

        return observableOf(empty());
      },

 enumerate() {
   return observableOf(queryResult);
 }