ember-cli-flash in acceptance test

controllers.application.js

import Ember from 'ember';

const { inject } = Ember;

export default Ember.Controller.extend({
  actions: {
    addFlashMessage() {
      this.get('flashMessages').info('just a test');
    }
  },
  flashMessages: inject.service(),
  appName: 'Ember Twiddle'
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
{{#each flashMessages.queue as |flash|}}
  {{flash-message flash=flash}}
{{/each}}
<button class="button" {{action 'addFlashMessage'}}>
  add flash messages
</button>

tests.acceptance.my-acceptance-test.js

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

moduleForAcceptance('TODO: put something here');

test('clicking the button renders flash', function(assert) {
  visit('/');
  
  andThen(() => {
    let button = find('.button');
    click(button);
  });

  andThen(function() {
    assert.ok(
      find('.alert').length
    );
  });
});

test('not clicking the button renders nothing', function(assert) {
  visit('/');

  andThen(function() {
    assert.notOk(
      find('.alert').length
    );
  });
});

tests.helpers.destroy-app.js

import Ember from 'ember';

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

tests.helpers.flash-message.js

import Ember from 'ember';
import FlashObject from 'ember-cli-flash/flash/object';

const { K } = Ember;

FlashObject.reopen({ init: K });

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.test-helper.js

import resolver from './helpers/resolver';
import './helpers/flash-message';
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": "2.6.2",
    "ember-data": "2.7.0",
    "ember-template-compiler": "2.6.2"
  },
  "addons": {
    "ember-cli-flash": "*"
  }
}