Why component scanning does not work for Spring Boot unit tests?

Question

The service class FooServiceImpl is annotated with @Service aka @Component which makes it eligible for autowiring. Why this class is not being pick

Answer 1

I had to solve a similar problem with a slight variation. Thought to share the details of that, thinking it might give choices to those who hit upon similar issues.

I wanted to write integration tests with only necessary dependencies loaded up instead of all of the app dependencies. So I chose to use @DataJpaTest, instead of @SpringBootTest. And, I had to include @ComponentScan too to parse the @Service beans. However, the moment ServiceOne started using a mapper bean from another package, I had to specify the specific packages to be loaded with @ComponentScan. Surprisingly, I even had to do this for the second service that does not auto-wire this mapper. I did not like that because it leaves the impression to the reader that this service depends on that mapper when it is actually not. So I realized that the package structure for services needs to be fine-tuned further to represent the dependencies more accurately.

To summarise, instead of @SpringBootTest, a combination of @DataJpaTest+@ComponentScan with package names can use to load just the layer-specific dependencies. This might even help us to fine-tune the design to represent your dependencies more accurately.

Design before

1. com.java.service.ServiceOneImpl

@Service
public class ServiceOneImpl implements ServiceOne {   
  @Autowired
  private RepositoryOne repositoryOne;    
  @Autowired
  private ServiceTwo serviceTwo;      
  @Autowired
  private MapperOne mapperOne;
}

2. com.java.service.ServiceTwoImpl

@Service
public class ServiceTwoImpl implements ServiceTwo {   
  @Autowired
  private RepositoryTwo repositoryTwo;    
}

3. ServiceOneIntegrationTest

@RunWith(SpringRunner.class)
@DataJpaTest
@ComponentScan({"com.java.service","com.java.mapper"})
public class ServiceOneIntegrationTest {

4. ServiceTwoIntegrationTest.java

@RunWith(SpringRunner.class)
@DataJpaTest
@ComponentScan({"com.java.service","com.java.mapper"})
public class ServiceTwoIntegrationTest {

After fine-tuning the package names

1. com.java.service.one.ServiceOneImpl

@Service
public class ServiceOneImpl implements ServiceOne {   
  @Autowired
  private RepositoryOne repositoryOne;    
  @Autowired
  private ServiceTwo serviceTwo;      
  @Autowired
  private MapperOne mapperOne;
}

2. com.java.service.two.ServiceTwoImpl

@Service
public class ServiceTwoImpl implements ServiceTwo {   
  @Autowired
  private RepositoryTwo repositoryTwo;    
}

3. ServiceOneIntegrationTest

@RunWith(SpringRunner.class)
@DataJpaTest
@ComponentScan({"com.java.service","com.java.mapper"})
public class ServiceOneIntegrationTest {

4. ServiceTwoIntegrationTest.java

@RunWith(SpringRunner.class)
@DataJpaTest
@ComponentScan({"com.java.service.two"}) // CHANGE in the packages
public class ServiceTwoIntegrationTest {