Injecting Mockito mocks into a Spring bean

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

Answer 1

I use a combination of the approach used in answer by Markus T and a simple helper implementation of ImportBeanDefinitionRegistrar that looks for a custom annotation (@MockedBeans) in which one can specify which classes are to be mocked. I believe that this approach results in a concise unit test with some of the boilerplate code related to mocking removed.

Here's how a sample unit test looks with that approach:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(loader=AnnotationConfigContextLoader.class)
public class ExampleServiceIntegrationTest {

    //our service under test, with mocked dependencies injected
    @Autowired
    ExampleService exampleService;

    //we can autowire mocked beans if we need to used them in tests
    @Autowired
    DependencyBeanA dependencyBeanA;

    @Test
    public void testSomeMethod() {
        ...
        exampleService.someMethod();
        ...
        verify(dependencyBeanA, times(1)).someDependencyMethod();
    }

    /**
     * Inner class configuration object for this test. Spring will read it thanks to
     * @ContextConfiguration(loader=AnnotationConfigContextLoader.class) annotation on the test class.
     */
    @Configuration
    @Import(TestAppConfig.class) //TestAppConfig may contain some common integration testing configuration
    @MockedBeans({DependencyBeanA.class, DependencyBeanB.class, AnotherDependency.class}) //Beans to be mocked
    static class ContextConfiguration {

        @Bean
        public ExampleService exampleService() {
            return new ExampleService(); //our service under test
        }
    }
}

To make this happen you need to define two simple helper classes - custom annotation (@MockedBeans) and a custom ImportBeanDefinitionRegistrar implementation. @MockedBeans annotation definition needs to be annotated with @Import(CustomImportBeanDefinitionRegistrar.class) and the ImportBeanDefinitionRgistrar needs to add mocked beans definitions to the configuration in it's registerBeanDefinitions method.

If you like the approach you can find sample implementations on my blogpost.