如何使用Guice将单元测试中的模拟对象注入到被测试的类中

Question

请考虑以下代码：

@Singleton
public class MyServiceImpl {
    public int doSomething() {
        return 5;
    }
}

@ImplementedBy(MyServiceImpl.class)
public interface MyService {
    public int doSomething();
}

public class MyCommand {
    @Inject private MyService service;

    public boolean executeSomething() {
        return service.doSomething() > 0;
    }
}

public class MyCommandTest {
    @InjectMocks MyServiceImpl serviceMock;
    private MyCommand command;

    @Before public void beforeEach() {
        MockitoAnnotations.initMocks(this);
        command = new MyCommand();
        when(serviceMock.doSomething()).thenReturn(-1); // <- Error here
    }

    @Test public void mockInjected() {
        boolean result = command.executeSomething();
        verify(serviceMock).doSomething();
        assertThat(result, equalTo(false));
    }
}

此外，出现此错误的原因可能是：1。您使用final/private/equals()/hashCode（）方法中的任一个作为存根。这些方法不能被截取/验证。不支持在非公共父类上声明的模拟方法。2.内部when（）不是对mock而是对其他对象调用method。

我是通过Guice进行依赖注入的新手，不知道为什么我不能以这种方式模拟实现对象？

Answer 1

一个简单的解决方案是将CDI与构造函数注入结合起来，而不用考虑Guice进行测试：

public class MyCommand {
    private final MyService service;

    @Inject
    public MyCommand(MyService service) {
        this.service = service;
    }

    public boolean executeSomething() {
        return service.doSomething() > 0;
    }
}

@RunWith(MockitoJUnitRunner.class)
public class MyCommandTest {
    @Mock
    MyServiceImpl serviceMock;
    private MyCommand command;

    @Before public void beforeEach() {
        MockitoAnnotations.initMocks(this);
        when(serviceMock.doSomething()).thenReturn(-1); // <- Error here

        // inject without Guice
        command = new MyCommand(serviceMock);
    }
}

否则，如果您不喜欢构造函数注入，测试代码应该如下所示：

@RunWith(MockitoJUnitRunner.class)
public class MyCommandTest {
    @Mock
    MyServiceImpl serviceMock;
    @InjectMocks 
    private MyCommand command;

    @Before 
    public void beforeEach() {
        MockitoAnnotations.initMocks(this);
        command = new MyCommand();
        when(serviceMock.doSomething()).thenReturn(-1); // <- Error here
    }
}