RxJS test without marbles diagrams

without-marbles.ts

it('multiplies each number by 2', done => {
  const numbers$ = interval(1000).pipe(
    take(3),
    map(n => n + 1)
  )
  // This emits: -1-2-3-|

  const numbersTwoTimes$ = numTwoTimes(numbers$)

  const results: number[] = []

  numbersTwoTimes$.subscribe(
    n => {
      results.push(n)
    },
    err => {
      done(err)
    },
    () => {
      expect(results).toEqual([2, 4, 6])
      done()
    }
  )
})