How to replace a bean with a testing mock in Spring Boot for integration testing

Question

I have a spring app and integration tests for this app. I would like to replace a bean with a mock bean.

My real bean looks like this

@Service
public class MyService {

}

and for testing I would like it to be replaced

@Service
public class TestMyService {

}

All I can think of is to use profiles for different services. For example:

@Service
@Profile("!test")
public class MyService implements IMyService {

}

@Service
@Profile("test")
public class TestMyService implements IMyService {

}

And then I autowire the bean like this

@Autowired
private IMyService myService;

Is there a better way?

Answer 1

Spring Boot has @MockBean and @SpyBean annotations exactly for this purpose:

https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-testing.html#boot-features-testing-spring-boot-applications-mocking-beans

Declaration is simple:

@MockBean
private MyService myService;

Spring Boot will inject Mockito mock there instead of the actual bean.

Answer 2

My personal preference is to avoid loading the compete context for testing. Therefore I like my test to focus on a subset of beans. It usually means I outline beans which I use in tests:

@RunWith(SpringRunner.class)
@SpringBootTest(
        classes = {TestMyService.class, OtherClassNeededForTesting.class}
)
public class DelaysProviderTest {

}

If more configuration is needed I tend to prepare a separate configuration class for tests:

@RunWith(SpringRunner.class)
@SpringBootTest(
        classes = MyTest.Cfg.class
)
public class MyTest {

    @Import({
        // .. some classes to import including TestMyService.class
    })
    @Configuration
    public static class Cfg {

    }

}

When even more configuration is needed (or mocking), I use the test configuration for providing appropriate mocks

@RunWith(SpringRunner.class)
@SpringBootTest(
        classes = MyTest.Cfg.class
)
public class MyTest {

    @Import({
        // .. some classes to import
    })
    @Configuration
    public static class Cfg {

        @Bean
        public IMyService service() {
            IMyService mock = Mockito.mock(IMyService.class);
            when(mock.someMethod()).thenReturn("some data");

            return mock;
        }

    }

}