FetchEvent#waitUntil in Jest context

Problem

The promises passed to FetchEvent.prototype.waitUntil cannot be retrieved via Response.prototype.waitUntil(). There doesn’t seem to be any other way to access them either, but if there is, the Writing and Running Tests docs don’t mention it.

Configuration

// jest.config.js
module.exports = {
  testEnvironment: 'miniflare',
}

Example Code

describe('waitUntil', () => {
  it('caches things', async () => {
    async function myHandler(fetchEvent) {
      const { url } = fetchEvent.request
      fetchEvent.waitUntil(caches.default.put(url, new Response('written to cache')))
      return new Response('returned from worker')
    }

    // build a FetchEvent:
    const url = 'https://example.com/cache-something'
    const request = new Request(url)
    const fetchEvent = new FetchEvent('fetch', { request })

    // get a response for it:
    const response = await myHandler(fetchEvent)

    // the response should have the Promises from `fetchEvent.waitUntil`:
    const awaited = await response.waitUntil()
    expect(awaited[0]).toBeTruthy() // this fails; awaited is []
    expect(await awaited[0].text()).toBe('written to cache')

    // and the cache-write should have completed:
    const cachedResponse = await caches.default.match(url)
    expect(cachedResponse).toBeTruthy()
    expect(await cachedResponse.text()).toBe('written to cache')
  })
})

[mrbbot]

Hey! 👋 Thanks for raising this. Will try get a getWaitUntil(event) method added and exposed to tests soon. 🙂

[jamesarosen]

@CraigglesO I poked at this a bit. I’m glad you did it because your #345 looks much better than what I had!