Integration testing
Finally, we can always write an integration test that will exercise the whole application, as shown in the following code:
describe('integration specs', () => {
 const initialData = {
   conversations: [
     {id: 1, title: 'The Myth of Sisyphus'},
     {id: 2, title: 'The Nicomachean Ethics'}
   ],
   messages: [
     {id: 1, conversationId: 1, text: 'The Path of the Absurd Man'}
   ]
 };
 beforeEach(async(() => {
   TestBed.configureTestingModule({
     // MailModule is an NgModule that contains all application
     // components and the router configuration
     // RouterTestingModule overrides the router and location providers
    ...
