activating "test isolation validation" and adding test to trigger it

Based on the following documentation:
https://github.com/emberjs/ember-qunit/blob/master/docs/TEST_ISOLATION_VALIDATION.md

Author: tsagadar

tests/test-helper.js

@@ -9,4 +9,6 @@ setApplication(Application.create(config.APP));
 
 setup(QUnit.assert);
 
-start();
+start({
+  setupTestIsolationValidation: true
+});

tests/unit/models/rental-test.js

@@ -1,5 +1,6 @@
 import { module, test } from 'qunit';
 import { setupTest } from 'super-rentals/tests/helpers';
+import { later } from '@ember/runloop';
 
 module('Unit | Model | rental', function (hooks) {
   setupTest(hooks);
@@ -37,4 +38,10 @@ module('Unit | Model | rental', function (hooks) {
     rental.category = 'Estate';
     assert.strictEqual(rental.type, 'Standalone');
   });
+
+  test('checking test isolation validation', function (assert) {
+    assert.expect(1);
+    later(() => {}, 1000);
+    assert.ok(true);
+  });
 });