testing readable stream (in jest) with delay for pushed values

I'm having trouble testing streams (with jest) when there is a delay involved. I did try using fakeTimers as well, but to no avail. Any pointers would be appreciated.

I have coded the below to have no dependencies - so the code should run standalone The first of the two tests works, but the secod one fails.

const Readable = require('stream').Readable
function sleep(ms) {return new Promise(resolve => setTimeout(resolve, ms))}
const lines = ['line 1\n', 'line 2\nline 3']
function* getIter() {for (let line of lines) {yield line}}

describe ('Iteration', () => {

  it ('read iter values from stream', () => {
    let rs = new Readable, res, iter = getIter()

    while (res = iter.next()) {
      if (res.done) {
        rs.push(null)
        break
      } else {
        rs.push(res.value)
      }
    }
    rs.pipe(process.stdout)
  })

  it ('read iter values from stream with delay', (done) => {
    var rs = new Readable,
        res,
        iter = getIter()

    while (res = iter.next()) {
      if (res.done) {
        sleep(1).then(() => {
          rs.push(null)
        })
        break
      } else {
        sleep(1).then(() => {
          rs.push(res.value)
        })
      }
    }

    sleep(10).then(() => {
      rs.pipe(process.stdout)
      done()
    })
  })
})