的Mockito - 嘲讽的接口 - 抛出NullPointerException异常 [英] mockito - mocking an interface - throwing NullPointerException

问题描述

我也嘲讽后获得空指针异常。请找我的项目结构。

I am getting null pointer exception after mocking also. Please find my project structure.

    //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();
        }
   }

我想在这里使用TDD，意味着我有写的服务接口，但没有实际执行。要测试listPets（）方法中，我清楚地知道它使用服务来获得宠物列表。但在这里我打算测试listPets App类的（）方法，所以我试图嘲弄服务接口。

I am trying to use TDD here, Means I have the service interface written, But not the actual implementation. To test the listPets() method, I clearly knows that its using the service to get the list of pets. But my intention here to test the listPets() method of the App class, Therefore I am trying to mock the service interface.

使用该服务，以获得宠物App类的listPets（）方法。因此我使用嘲讽的Mockito那部分。

The listPets() method of the App class using the service to get the pets. Therefore I am mocking that part using mockito.

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

但是，当单元测试运行时，perService.listPets（）抛出的 NullPointerException异常这是我使用上述 Mockito.when code嘲笑。你能帮我在这？

But when the unit test is running , perService.listPets() throwing NullPointerException which I have mocked using the above Mockito.when code. Could you please help me on this?

推荐答案

NullPointerException异常是因为，在应用程序，petService是不是想使用它之前实例化。注入模拟，在应用中添加这个方法：

NullPointerException is because, in App, petService isn't instantiated before trying to use it. To inject the mock, in App, add this method:

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

然后在您的测试，请致电：

Then in your test, call:

app.setPetService(petService);

运行前 app.listPets（）;

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