mock the server response even the server is unreachable

Things I know (please correct me if I'm wrong, thank you :)):

• HttpInterceptor works in a way similar to Aspect-oriented programming;
• adding/modifying httpOptions can be achieved for requests;
• modifying the response with clone() can also be achieved for response;

My problems

I want to test some libraries while their related servers can be down sometimes when developing I just care about the data no interaction with server is okay

Is it possible that I can just return a mock data already prepared without requesting the server when the request met some patterns even the service lies in other libraries?

My Requirements

• all the logic in the libraries stays the same;
• using the mock data to respond to the http request from the libraries;

Updated 2019-01-15

Thanks to the help of @Sachin Gupta, I tested the interceptor further with this demo.

What have been done:

• auth-interceptor.ts to add headers for the request;
• logging-interceptor.ts added to track the request details and time cost;
• data-mocking-interceptor.ts to stop the request to the server and return the mock data directly.

Have a look at this.

https://stackblitz.com/edit/angular-json-http-response-catch

If the server is reachable, the data is populated, otherwise mocked is sent as response

Interceptor

export class NoopInterceptor implements HttpInterceptor {

  intercept(req: HttpRequest<any>, next: HttpHandler):
    Observable<HttpEvent<any>> {
      let response = new HttpResponse();
      response = response.clone({body: [{"sads":"ewre"}]});
   
    return next.handle(req).pipe(catchError((err) => {return of(response).pipe(delay(10))}) );
  }
}