New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  tree: [{
    id: 0,
    name: 'Root',
    isExpanded: true,
    isSelected: false,
    isVisible: true,
    children: [
      {
        id: 1,
        name: 'First Child',
        isExpanded: true,
        isSelected: false,
        isVisible: true,
        children: []
      },
      {
        id: 2,
        name: 'Second Child',
        isExpanded: true,
        isSelected: false,
        isVisible: true,
        children: [
          {
            id: 3,
            name: 'First Grand Child',
            isExpanded: true,
            isSelected: true,
            isVisible: true,
            children: []
          }
        ]
      }
    ]
  }]
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
{{tree}}
{{x-tree model=tree}}
<br>
<br>
{{outlet}}
<br>
<br>

tests.helpers.destroy-app.js

import { run } from '@ember/runloop';

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

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.autoboot = true;
  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 Application from '../app';
import config from '../config/environment';
import { setApplication } from '@ember/test-helpers';
import { start } from 'ember-qunit';
import { assign } from '@ember/polyfills';

let attributes = assign({ rootElement: '#main' }, config.APP);
setApplication(Application.create(attributes));

start();

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2",
    "ember-simple-tree": "0.7.0"
  }
}