Mock manual

Book.java

public class Book {
   private String titulo;
   public Book(String titulo) {
	 this.titulo = titulo;
   }
   public String getTitulo() {
	 return titulo;  
   }
}

BookSearch.java

import org.json.JSONObject;

public class BookSearch {
	
   BookService rbs;
   
   public BookSearch(BookService rbs) {
	 this.rbs = rbs;
   }
   
   public Book getBook(int isbn) {
	 String json = rbs.search(isbn);
	 JSONObject obj = new JSONObject(json);
	 String titulo = (String) obj.get("titulo");
	 return new Book(titulo);
   }
}

BookSearchTest.java

import static org.junit.Assert.*;
import org.junit.*;

class BookConst {
   public static final String ESM = "{ \"titulo\": \"Eng Soft Moderna\" }";	
   public static final String NULLBOOK = "{ \"titulo\": \"NULL\" }";

}

class MockBookService implements BookService {
   public String search(int isbn) { 
	 if (isbn == 1234) 
  		return BookConst.ESM;
	 return BookConst.NULLBOOK;
   }
}

public class BookSearchTest {
    
	BookService service1;
	
	@Before
	public void init() {
	   service1 = new MockBookService();	
	}
	
	@Test
	public void testGetBook() {
		BookSearch bs = new BookSearch(service1);
		String titulo = bs.getBook(1234).getTitulo();
		assertEquals("Eng Soft Moderna", titulo);
	}
}

BookService.java

public interface BookService {
  String search(int isbn);
}