yield

components.button-group-item.js

import Ember from 'ember';

export default Ember.Component.extend({
  // layout,
  tagName: 'button',
  classNames: [ 'group-btn' ],
  classNameBindings: [ 'isSelected:active' ],
  
  model: null,
  
  isSelected: Ember.computed('model', 'selection', function isSelected() {
    return this.get('model') === this.get('selection')
  }),
  
  
}).reopenClass({
  positionalParams: ['model']
});

components.button-group.js

import Ember from 'ember';

export default Ember.Component.extend({
  
  actions: {
  	onSelect(selection) {
      this.get('onSelect')(selection);
    }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  foo: 'bar',
  
  selection: 'btn-1',
  
  init () {
    this._super(...arguments);
    
    this.set('items', [
      { name: 'foo' },
      { name: 'bar', selected: true },
      { name: 'qux' }
    ]);
  },
  
  actions: {
  	update(selection) {
    	this.set('selection', selection)
    }
  }
});

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.selected {
	background: blue;
}

templates.application.hbs

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

{{container-list items=items}}

{{#container-list items=items customButton="list-item" as |item|}}
	{{item.button data=item.data}}
{{/container-list}}



{{#button-group onSelect=(action "update") as |bg|}}
	{{bg.button "btn-1" on}}
  {{bg.button "btn-2"}}
{{/button-group}}

<br>
<br>

templates.components.button-group-item.hbs

{{yield}}

templates.components.button-group.hbs

{{yield (hash
  button=(component "button-group-item" selection=selection buttonGroup=this onClick=(action "onSelect"))
	onSelect=(action "onSelect")
)}}

templates.components.container-list.hbs

<div class="list">
	{{#each items as |item|}}
  	{{#if customButton}}
      {{yield (hash
      	button=(component customButton)
        data=item
      )}}
    {{else}}
    	<button class={{if item.selected "selected" "plain"}}>{{item.name}}</button>
    {{/if}}
  {{/each}}
</div>

templates.components.list-item.hbs

<div class="item">
	{{data.name}}
</div>

tests.helpers.destroy-app.js

import Ember from 'ember';

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

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": "0.13.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.16.2",
    "ember-template-compiler": "2.16.2",
    "ember-testing": "2.16.2"
  },
  "addons": {
    "ember-data": "2.16.3"
  }
}