registerWaiter on component directly

components.async-image-wrapper.js

import Ember from 'ember';

export default Ember.Component.extend({
  imageLoaded: 'image loading',
  imageWidth: 'width loading',
  
  // purely to make sure image loads each time and
  // is not cached for testing
  volatileSrc: Ember.computed('src', function(){
    return this.get('src') + '?cache=' + new Date().toISOString();
  }),
  
  actions: {
    imageLoaded(message, width) {
      if (!this.isDestroyed) {
        this.set('imageLoaded', message);
        this.set('imageWidth', width);
      }
    }
  }
});

components.async-image.js

import Ember from 'ember';

export default Ember.Component.extend({
  tagName: 'img',
  attributeBindings: ['src'],
  
  init() {
    this._super(...arguments);
    
    if (Ember.testing) {
      this._loading = false;
      Ember.Test.registerWaiter(() => this._loading === false);
    }
  },
  
  load(src) {
    let promise = new Ember.RSVP.Promise((resolve, reject) => {
      const img = new Image();
      img.src = src;
      img.onload = e => {
        Ember.run(() => resolve(img));
      };
      img.onerror = () => {
        Ember.run(() => reject());
      };
    });
    
    if (Ember.testing) {
    	this._loading = true;
      return promise.finally(() => this._loading = false);
    }
    
    return promise;
  },
  
  loadImage() {
    let src= this.get('src');
    
    this.load(src).then(img => {
      this.get('onImageLoad')("image loaded", img.width);
    })
    .catch(error => {
      Ember.Logger.log('error', error);
      this.get('onImageLoad')("image could not load");
    });
  },

  didInsertElement() {
    Ember.run.scheduleOnce('afterRender', this, this.loadImage);
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
});

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

h1, h2 {
  //display: none;
}

templates.application.hbs

<h1>Testing async behaviour</h1>
<h2>Using wait() in integration tests</h2>
<p>I thought that by using a promise or the run loop then the wait helper would pause before checking the assertion, but it only works with run.later and I can't work out why.</p>
{{async-image-wrapper src='https://emberjs.com/images/tomsters/sandiego-zoey-b7637d09.png'}}

templates.components.async-image-wrapper.hbs

{{async-image src=volatileSrc onImageLoad=(action 'imageLoaded')}}
<p id="image-loaded-text">{{imageLoaded}}</p>
<p>width: <span id="image-width-text">{{imageWidth}}</span></p>

tests.acceptance.async-image-test.js

import { test } from 'qunit';
import moduleForAcceptance from '../../tests/helpers/module-for-acceptance';

moduleForAcceptance('Waits for image to be loaded');

test('/', function(assert) {
  visit('/');

  andThen(function() {
    assert.equal(currentURL(), '/');
    assert.equal(find('#image-loaded-text').text(), 'image loaded');
    assert.equal(find('#image-width-text').text(), '412');   
  });
});

tests.helpers.destroy-app.js

import Ember from 'ember';

export default function destroyApp(application) {
  Ember.run(application, 'destroy');
}

tests.helpers.module-for-acceptance.js

import { module } from 'qunit';
import Ember from 'ember';
import startApp from '../helpers/start-app';
import destroyApp from '../helpers/destroy-app';

const { RSVP: { Promise } } = Ember;

export default function(name, options = {}) {
  module(name, {
    beforeEach() {
      this.application = startApp();

      if (options.beforeEach) {
        return options.beforeEach.apply(this, arguments);
      }
    },

    afterEach() {
      let afterEach = options.afterEach && options.afterEach.apply(this, arguments);
      return Promise.resolve(afterEach).then(() => destroyApp(this.application));
    }
  });
}

tests.helpers.resolver.js

import Resolver from '../../resolver';
import config from '../../config/environment';

const resolver = Resolver.create();

resolver.namespace = {
  modulePrefix: config.modulePrefix,
  podModulePrefix: config.podModulePrefix
};

export default resolver;

tests.helpers.start-app.js

import Ember from 'ember';
import Application from '../../app';
import config from '../../config/environment';

const { run } = Ember;
const assign = Ember.assign || Ember.merge;

export default function startApp(attrs) {
  let application;

  let attributes = assign({rootElement: "#test-root"}, config.APP);
  attributes = assign(attributes, attrs); // use defaults, but you can override;

  run(() => {
    application = Application.create(attributes);
    application.setupForTesting();
    application.injectTestHelpers();
  });

  return application;
}

tests.integration.components.async-image-wrapper-test.js

import { moduleForComponent, test } from 'ember-qunit';
import wait from 'ember-test-helpers/wait';
import hbs from 'htmlbars-inline-precompile';

moduleForComponent('async-image-wrapper', 'Uses Promise', {
  integration: true
});

test('If image found update message to success', function(assert) {
  assert.expect(2);
  
  this.render(hbs`{{async-image-wrapper src='https://emberjs.com/images/tomsters/sandiego-zoey-b7637d09.png'}}`);
  
  return wait().then( () => {
    assert.equal(this.$('#image-loaded-text').text(), 'image loaded');
    assert.equal(this.$('#image-width-text').text(), '412');
  });
});

tests.test-helper.js

import resolver from './helpers/resolver';
import {
  setResolver
} from 'ember-qunit';

setResolver(resolver);

twiddle.json

{
  "version": "0.10.4",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": true
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.6.0",
    "ember-data": "2.6.0",
    "ember-template-compiler": "2.6.0"
  },
  "addons": {}
}