Mockito 将模拟注入 Spy 对象

I'm writing a test case for a Class which has a 2 level of dependency injection. I use @Spy annotation for the 1 level dependency injection object, and I would like to Mock the 2nd level of injection. However, I kept getting null pointer exception on the 2nd level. Is there any way that I inject the mock into the @Spy object?

public class CarTestCase{
    @Mock
    private Configuration configuration;

    @Spy 
    private Engine engine;

    @InjectMocks 
    private Car car;

    @Test
    public void test(){

       Mockito.when(configuration.getProperties("")).return("Something");
       car.drive();
    }

}

public class Car{
    @Inject
    private Engine engine;

    public void drive(){
        engine.start();
    }
}

public class Engine{
    @Inject 
    private Configuration configuration;

    public void start(){
        configuration.getProperties();   // null pointer exception
    }

}

推荐答案

Mockito 不能执行如此棘手的注入，因为它不是一个注入框架.因此，您需要重构代码以使其更具可测试性.使用构造函数注入很容易做到:

public class Engine{
    private Configuration configuration;

    @Inject 
    public Engine(Configuration configuration) {
        this.configuration = configuration;
    }
    ........
}

public class Car{
    private Engine engine;

    @Inject    
    public Car(Engine engine) {
        this.engine = engine;
    }
}

public class CarTestCase{

    private Configuration configuration;

    private Engine engine;

    private Car car;

    @Before
    public void setUp(){
        configuration = mock(Configuration.class);
        engine = spy(new Engine(configuration));
        car = new Car(engine);
    }

    @Test
    public void test(){

       Mockito.when(configuration.getProperties("")).return("Something");
       car.drive();
    }

}