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
     ...