mockito-模拟接口-抛出NullPointerException

Question

    //this is the pet interface
    public interface Pet{
    }

    // An implementation of Pet
    public class Dog extends Pet{
        int id,
        int petName;

    }
    // This is the Service Interface
    public interface PetService {
        List<Pet> listPets();
    }

    // a client code using the PetService to list Pets
    public class App {
        PetService petService;

        public void listPets() {
             // TODO Auto-generated method stub
             List<Pet> listPets = petService.listPets();
             for (Pet pet : listPets) {
                System.out.println(pet);
             }
        }
    }

    // This is a unit test class using mockito
    public class AppTest extends TestCase {

        App app = new App();
        PetService petService = Mockito.mock(PetService.class);
        public void testListPets(){
            //List<Pet> listPets = app.listPets();
            Pet[] pet = new Dog[]{new Dog(1,"puppy")};
            List<Pet> list = Arrays.asList(pet);
            Mockito.when(petService.listPets()).thenReturn(list);
            app.listPets();
        }
   }

    Mockito.when(petService.listPets()).thenReturn(list);

Answer 1

NullPointerException是因为在应用程序中，在尝试使用petService之前没有实例化它。要注入mock，在App中，添加以下方法：

public void setPetService(PetService petService){
    this.petService = petService;
}

然后在测试中调用：

app.setPetService(petService);

运行app.listpets()；之前