State leakage via class arrays/objects

controllers.application.js

import Ember from 'ember';

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

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.dummy-test.js

import { module } from 'qunit';
import { test } from 'ember-qunit';

module('Demonstate state leakage');

var Person = Ember.Object.extend({
  groceryList: ['eggs', 'tuna']
});

test('Shared array can be modified', function(assert) {
  let bob = Person.create({name: 'Bob'});
  
  bob.get('groceryList').popObject();
  
  assert.deepEqual(bob.get('groceryList'), ['eggs']);
});

test('The array mutation persists across tests', function (assert) {
  let jill = Person.create({name: 'Jill'});
  
  assert.deepEqual(jill.get('groceryList'), ['eggs', 'tuna'], 'the mutation persists');
});

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"
  }
}