Why does autowired repository result in a NullPointerException in Junit4 context?

Question

I'm new to Java development so sorry in advance if I'm not using the appropriate terms.

Whenever I run a test on a class that needs to save something in my database, I face a NullPointerException on the Autowired repository.

I use Junit4, here are code snippets:

application-test.properties

spring.datasource.url=jdbc:tc:mysql:8.0.29://localhost:3306/MYSERVICE

MyService.java

@Component
class MyService {
    @Autowired MyRepository myRepository;
    
    public void mainFunction() {
        myRepository.saveSomething();
    }
}

MyRepository.java

@Repository
public interface MyRepository extends JpaRepository<T, Long> {
    
    void saveSomething();
}

MyServiceTest.java

public class myServiceTest extends  TestConfiguration {
    @Rule
    public MySQLContainer mysql = new MySQLContainer();

    @InjectMocks MyService myService;

    @Test
    public void mainFunctionTest() {
        myService.mainFunction()
    }
}

MyServiceTestApplication.java

@SpringBootApplication(exclude = {
        DataSourceAutoConfiguration.class
})
public class MyServiceTestApplication{
}

TestConfiguration.java

@RunWith(SpringRunner.class)
@SpringBootTest(classes = MyServiceTestApplication.class)
@ActiveProfiles("test")
public abstract class TestConfiguration {

}

When I run the test in debug mode, I can see that myRepository is null

Any help would be highly appreciated

Thanks:)

Edit 01/08/2022: Add @Component on MyService

Edit 01/08/2022 (2): Add MyServiceTestApplication.java and TestConfiguration.java

Answer 1

It seems, you forgot to annotate the class MyService with @Service .

With this annotation being made at that class, the Spring framework will recognize it:

This annotation serves as a specialization of @Component, allowing for implementation classes to be autodetected through classpath scanning.

Given that the rest of the configuration is working, the @Autowired dependency injection mechanism will hereby provide you with an instance of the @Repository you requested, at runtime, here your test setup.