New Twiddle

models.group.js

import Model from "ember-data/model";
import attr from "ember-data/attr";
import { belongsTo, hasMany } from "ember-data/relationships";

export default Model.extend({
  owner: belongsTo('user'),
  invitations: hasMany('invitations', { inverse: 'group' }),

  memberships: Ember.computed.filterBy('invitations', 'accepted', true),
  pendingInvitations: Ember.computed.filterBy('invitations', 'accepted', false),

  members: Ember.computed('[email protected]', function() {
    return this.get('invitations').filterBy('accepted', true).getEach('member');
  }),
});

models.invitation.js

import Model from "ember-data/model";
import attr from "ember-data/attr";
import { belongsTo, hasMany } from "ember-data/relationships";

export default Model.extend({
  accepted: attr({ defaultValue: null }),
  group: belongsTo('group'),
  member: belongsTo('user')
});

models.user.js

import Model from "ember-data/model";
import attr from "ember-data/attr";
import { belongsTo, hasMany } from "ember-data/relationships";

export default Model.extend({
  username: attr('string'),
  invitations: hasMany('invitations', { inverse: 'member' }),
});

routes.index.js

import Ember from 'ember';

export default Ember.Route.extend({
  model() {
    return Ember.RSVP.hash({
      user: this.store.find('user', 1),
    });
  },

  afterModel: function(model) {
    if (model.user) {
      return model.user.get('invitations').then((invitations) => (
        Ember.RSVP.all(
          invitations.map((invitation) => (
            invitation.get('group').then(group => {
              return group.reload(); // makes the test hang
            })
          ))
        )
      ));
    }
  },
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

templates.index.hbs

Everything is loaded!

tests.acceptance.index-test.js

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

moduleForAcceptance('Acceptance | Index');

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

  andThen(function() {
    assert.equal(currentURL(), '/');
  });
});

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.test-helper.js

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

setResolver(resolver);

twiddle.json

{
  "version": "0.10.5",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": true
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.8.0",
    "ember-data": "2.8.0",
    "ember-template-compiler": "2.8.0",
    "ember-testing": "2.8.0"
  },
  "addons": {}
}