upgrade ember-qunit integration per Ember CLI v6.2 blueprints

Author: jelhan

test-app/tests/test-helper.ts

@@ -3,10 +3,12 @@ import config from 'test-app/config/environment';
 import * as QUnit from 'qunit';
 import { setApplication } from '@ember/test-helpers';
 import { setup } from 'qunit-dom';
-import { start } from 'ember-qunit';
+import { loadTests } from 'ember-qunit/test-loader';
+import { start, setupEmberOnerrorValidation } from 'ember-qunit';
 
 setApplication(Application.create(config.APP));
 
 setup(QUnit.assert);
-
+setupEmberOnerrorValidation();
+loadTests();
 start();