Puzzled about how whenCurrentJobsFinished is supposed to work

bull-test.js

const Queue = require('bull')
const q = new Queue('test')

const main = async () => {
  await q.clean(0, 'completed')
  q.process(async job => {
    console.log('work starting')
    await new Promise(resolve => setTimeout(resolve, 3000))
    console.log('work done')
  })
  q.on('completed', async job => {
    console.log('on completed', await q.getJobCounts())
  })
  console.log('add job')
  await q.add({}) 
  console.log('wait', await q.getJobCounts())
  const x = await q.whenCurrentJobsFinished()
  console.log('waited', await q.getJobCounts())
  await new Promise(resolve => setTimeout(resolve, 1000))
  console.log('close', await q.getJobCounts())
  await q.close()
  console.log('closed')
}
main().catch(err => console.error(err))

output

add job
wait {
  waiting: 1,
  active: 0,
  completed: 0,
  failed: 0,
  delayed: 0,
  paused: 0
}
waited {
  waiting: 1,
  active: 0,
  completed: 0,
  failed: 0,
  delayed: 0,
  paused: 0
}
work starting
close {
  waiting: 0,
  active: 1,
  completed: 0,
  failed: 0,
  delayed: 0,
  paused: 0
}
work done
on completed {
  waiting: 0,
  active: 0,
  completed: 1,
  failed: 0,
  delayed: 0,
  paused: 0
}
closed