Ember concurrency timeout hanging in qunit

问题

In Ember I have a component that starts a never-ending poll to keep some data up to date. Like so:

export default Component.extend({
  pollTask: task(function * () {
    while(true) {
      yield timeout(this.get('pollRate'));
      this.fetchSomeData();
    }
  }).on('init')
})

This causes a preexisting acceptance test to get stuck in this task and run forever, even though it should be run asynchronously. The test looks like this:

test('my test', async function(assert) {
  mockFindRecord(make('fetched-model'));

  await visit('/mypage'); // gets stuck here
  await typeIn('input', 'abc123');

  assert.ok(somethingAboutThePage);
});

I thought at first that I had mocked the request wrong and that the test was just timing out, but it was in fact correctly polling data. Removing this task makes the acceptance test finish normally.

Testing this manually seems to work fine, and nothing gets stuck. Why is this happening and what is the right way to address this?

Saw Unit testing ember-concurrency tasks and yields but it doesn't really help since it only deals with unit tests.

回答1:

You're not doing anything wrong and this is a common gotcha with ember-concurrency. Ember-concurrency's timeout() function relies on Ember.run.later() to create the timeout and fortunately or unfortunately, Ember's test suite is aware of all timers created with Ember.run.later() and will wait for all timers to settle before letting the test continue. Since your code is using an infinite loop your timers will never settle so the test hangs. There's a nice little section about testing asynchronous code in the Ember guides here.

There's a section in the ember-concurrency docs about this exact problem here. I recommend you look through it to see their recommendations on how to tackle this although it seems as if there's no real elegant solution at the time.

The quickest and probably easiest way to get this to not hang would be to throw in a check to see if the app is being tested (gross, I know):

pollTask: task(function * () {
    while(true) {
      yield timeout(this.get('pollRate'));
      this.fetchSomeData();
      if (Ember.testing) return; // stop polling to prevent tests from hanging
    }
  }).on('init')

You can also try to throw in a call to Ember.run.cancelTimers() in your tests/helpers/start-app.js file (another suggestion in that section):

window._breakTimerLoopsId = Ember.run.later(() => {
  Ember.run.cancelTimers();
}, 500);

But it doesn't seem to appear in the API docs so I personally wouldn't rely on it.

来源：https://stackoverflow.com/questions/58513617/ember-concurrency-timeout-hanging-in-qunit