Any easy way to test Ember loading substates?

Is there a easy way in the route so I can test loading substates in Ember 2

I have tried this but it doesn't work. In the originating route, I have:

  actions: {
    willTransition(transition) {
      this.sleep(5000);
    }
  },
  sleep(time) {
    return new RSVP.Promise((resolve) => setTimeout(resolve, time));
  }