Testing Async Polling with Jasmine/Karma

I have this async function for polling a status url and resolving a promise once the result is no longer pending.

// asynchronously poll until we get a success or failure
function pollVerificationStatus(statusUrl) {
  return fetch(statusUrl)
    .then(function(response) {
      return response.json()
    }).then(function(response) {
      if (response.status === "pending") {
        return timeoutPromise(POLL_INTERVAL_MS)
          .then(function() {
            return pollVerificationStatus(statusUrl)
          })
      } else {
        return response
      }
    })
}

Its a pretty simple function but its very hard to test because theres a setTimeout inside a promise and theres all this deferring going on. Here's what I have so far, but it doesnt work..

function jsonResponsePromise(obj) {
  return new Promise(function(resolve) {
    resolve({
      json: function() {
        return new Promise(function(resolve2) {
          resolve2(obj)
        })
      }
    })
  })
}

describe("User Verification Polling", function() {
  beforeAll(function() {
    jasmine.clock().install()
    let count = 0
    spyOn(window, 'fetch').and.callFake(function() {
      count += 1
      return (count % 2 === 0) ? jsonResponsePromise({status:'ok'}) : jsonResponsePromise({status:'pending'})
    })
  })

  afterAll(function() {
    jasmine.clock().uninstall()
  })

  it("pollVerificationStatus()", function() {
    let x = pollVerificationStatus()
    jasmine.clock().tick(POLL_INTERVAL_MS+1)
    return x.then(function(response) {
      expect(window.fetch.calls.count()).toEqual(2)
    })
  })
})