example for https://stackoverflow.com/questions/54824239/observable-unit-test-passing-when-it-should-be-failing

index.js

const { rxObserver } = require('api/v0.3');
const { timer, throwError, of } = require('rxjs');
const { catchError, switchMap } = require('rxjs/operators');

const error$ = timer(5).pipe(
    switchMap(() => throwError('X'))
  );

error$.subscribe(rxObserver('Error'));

error$
  .pipe(
    catchError(err =>
      'Hello'
    )
  )
  .subscribe(rxObserver('Returned value'));

error$
  .pipe(
    catchError(err =>
      of('Hello')
    )
  )
  .subscribe(rxObserver('Returned Observable'));