Question du test Angular

@Component({ ... })
export class AppComponent {
  constructor(private userService: UserService){
     userService.getMessages().subscribe(messages => ...).unsubscribe();
  }
}

@Component({ ... })
export class AppComponent {
  constructor(private userService: UserService){
     const subscription = userService.getMessages().subscribe(messages => ...);
     subscription.close()
  }
}

@Component({ ... })
export class AppComponent implements OnDestroy {
  this.subscription: Subscription<any>;

  constructor(private userService: UserService){
     this.subscription = userService.getMessages().subscribe(messages => ...);
  }

  ngOnDestroy() {
     this.subscription.unsubscribe()
  }
}

@Component({ ... })
export class AppComponent implements OnDestroy {
  this.subscription: Observable<any>;

  constructor(private userService: UserService){
     this.subscription = userService.getMessages()
		 this.subscription.subscribe(messages => ...);
  }

  ngOnDestroy() {
     this.subscription.unsubscribe()
  }
}