class, the interface will still use mock
 data but exhibit the delays and errors that a real network would face.
 <p>
 Create an API interface and a mock implementation of it.
 <pre>
   public interface UserService {
     &#64;GET("/user/{id}")
     User getUser(@Path("id") String userId);
   }
   public class MockUserService implements UserService {
     &#64;Override public User getUser(String userId) {
       return new User("Jake");
     }
   }
 </pre>
 Given a <a href="http://github.com/square/retrofit