QUnit grouping failure

controllers.application.js

import Ember from 'ember';

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

controllers.my-controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
});

my-component.component.js

import Ember from 'ember';

export default Ember.Component.extend({
});

my-component.template.hbs

{{yield}}

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.controllers.my-controller-test.js

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

moduleFor('controller:my-controller', 'TODO: put something here', {
});

// Comment out this line, and it works fine.
// This should work fine, according to  http://api.qunitjs.com/QUnit/module
// module('Group A');
test('it exists', function(assert) {
  let controller = this.subject();
  assert.ok(controller);
});

// This also doesn't work
//module('Group A', function() {
//  test('it exists', function(assert) {
//    let controller = this.subject();
//    assert.ok(controller);
//  });
//});

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": true
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}