@uppy/utils/src/RateLimitedQueue.test.js

const RateLimitedQueue = require('./RateLimitedQueue')

const delay = ms => new Promise(resolve => setTimeout(resolve, ms))

describe('RateLimitedQueue', () => {
  let pending = 0
  function fn () {
    pending++
    return delay(15).then(() => pending--)
  }

  it('should run at most N promises at the same time', async () => {
    const queue = new RateLimitedQueue(4)
    const fn2 = queue.wrapPromiseFunction(fn)

    const result = Promise.all([
      fn2(), fn2(), fn2(), fn2(),
      fn2(), fn2(), fn2(), fn2(),
      fn2(), fn2()
    ])

    expect(pending).toBe(4)

    await delay(10)
    expect(pending).toBe(4)

    await result
    expect(pending).toBe(0)
  })

  it('should accept Infinity as limit', () => {
    const queue = new RateLimitedQueue(Infinity)
    const fn2 = queue.wrapPromiseFunction(fn)

    const result = Promise.all([
      fn2(), fn2(), fn2(), fn2(),
      fn2(), fn2(), fn2(), fn2(),
      fn2(), fn2()
    ])

    expect(pending).toBe(10)

    return result.then(() => {
      expect(pending).toBe(0)
    })
  })

  it('should accept non-promise function in wrapPromiseFunction()', () => {
    const queue = new RateLimitedQueue(1)
    function syncFn () { return 1 }
    const fn2 = queue.wrapPromiseFunction(syncFn)

    return Promise.all([
      fn2(), fn2(), fn2(), fn2(),
      fn2(), fn2(), fn2(), fn2(),
      fn2(), fn2()
    ])
  })
})