Injecting Mockito mocks into a Spring bean – Dev

The best answers to the question “Injecting Mockito mocks into a Spring bean” in the category Dev.

QUESTION:

I would like to inject a Mockito mock object into a Spring (3+) bean for the purposes of unit testing with JUnit. My bean dependencies are currently injected by using the @Autowired annotation on private member fields.

I have considered using ReflectionTestUtils.setField but the bean instance that I wish to inject is actually a proxy and hence does not declare the private member fields of the target class. I do not wish to create a public setter to the dependency as I will then be modifying my interface purely for the purposes of testing.

I have followed some advice given by the Spring community but the mock does not get created and the auto-wiring fails:

<bean id="dao" class="org.mockito.Mockito" factory-method="mock">
    <constructor-arg value="com.package.Dao" />
</bean>

The error I currently encounter is as follows:

...
Caused by: org...NoSuchBeanDefinitionException:
    No matching bean of type [com.package.Dao] found for dependency:
    expected at least 1 bean which qualifies as autowire candidate for this dependency.
    Dependency annotations: {
        @org...Autowired(required=true),
        @org...Qualifier(value=dao)
    }
at org...DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(D...y.java:901)
at org...DefaultListableBeanFactory.doResolveDependency(D...y.java:770)

If I set the constructor-arg value to something invalid no error occurs when starting the application context.

ANSWER:

@InjectMocks
private MyTestObject testObject;

@Mock
private MyDependentObject mockedObject;

@Before
public void setup() {
        MockitoAnnotations.initMocks(this);
}

This will inject any mocked objects into the test class. In this case it will inject mockedObject into the testObject. This was mentioned above but here is the code.

ANSWER:

The best way is:

<bean id="dao" class="org.mockito.Mockito" factory-method="mock"> 
    <constructor-arg value="com.package.Dao" /> 
</bean> 

Update
In the context file this mock must be listed before any autowired field depending on it is declared.

ANSWER:

Given:

@Service
public class MyService {
    @Autowired
    private MyDAO myDAO;

    // etc
}

You can have the class that is being tested loaded via autowiring, mock the dependency with Mockito, and then use Spring’s ReflectionTestUtils to inject the mock into the class being tested.

@ContextConfiguration(classes = { MvcConfiguration.class })
@RunWith(SpringJUnit4ClassRunner.class)
public class MyServiceTest {
    @Autowired
    private MyService myService;

    private MyDAO myDAOMock;

    @Before
    public void before() {
        myDAOMock = Mockito.mock(MyDAO.class);
        ReflectionTestUtils.setField(myService, "myDAO", myDAOMock);
    }

    // etc
}

Please note that before Spring 4.3.1, this method won’t work with services behind a proxy (annotated with @Transactional, or Cacheable, for example). This has been fixed by SPR-14050.

For earlier versions, a solution is to unwrap the proxy, as described there: Transactional annotation avoids services being mocked (which is what ReflectionTestUtils.setField does by default now)

ANSWER:

I have a very simple solution using Spring Java Config and Mockito:

@Configuration
public class TestConfig {

    @Mock BeanA beanA;
    @Mock BeanB beanB;

    public TestConfig() {
        MockitoAnnotations.initMocks(this); //This is a key
    }

    //You basically generate getters and add @Bean annotation everywhere
    @Bean
    public BeanA getBeanA() {
        return beanA;
    }

    @Bean
    public BeanB getBeanB() {
        return beanB;
    }
}