New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

mixins.prepare-next.js

import Ember from 'ember';

export default Ember.Mixin.create({
  setNext: function() {
    let currentStep = this.controllerFor('document').get('currentStep');

    if (currentStep === 'First_step') {
      //do something
    } else {
      //do something else...
    }
    // Bunch more stuff happens...
  }
});

templates.application.hbs

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

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.test-helper.js

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

setResolver(resolver);

tests.unit.mixins.prepare-next-test.js

import Ember from 'ember';
import PrepareNext from '../../../mixins/prepare-next';
import { module, test } from 'qunit';

module('mixin:prepare-next');

const PrepareNextObject = Ember.Object.extend(PrepareNext);



let subject;


test('#setNext does all the things', function(assert) {
  assert.expect(2);
  
  subject = PrepareNextObject.create();
  subject.controllerFor = () => {
    assert.ok(true, 'controllerFor called');
    return {
      get() {
        assert.ok(true, 'Get called');
        return 'First_step';
      }
    }
  };
  subject.setNext();
  //assert.equal(foo, bar);
});

twiddle.json

{
  "version": "0.8.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": true
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.5.1",
    "ember-data": "2.5.2",
    "ember-template-compiler": "2.5.1"
  }
}