Merge pull request emberjs#2257 from bgentry/patch-1

Add missing Service import to component test guide

source/testing/testing-components.md

@@ -321,6 +321,7 @@ import { module, test } from 'qunit';
 import { setupRenderingTest } from 'ember-qunit';
 import { render } from '@ember/test-helpers';
 import hbs from 'htmlbars-inline-precompile';
+import Service from '@ember/service';
 
 //Stub location service
 const locationStub = Service.extend({