What is @DataJpaTest and how does it test the repository layer? @DataJpaTest क्या है और यह रिपॉज़िटरी लेयर को कैसे टेस्ट करता है?

@DataJpaTest loads only the JPA-related components — @Entity classes, Spring Data repositories, and the DataSource — without loading services or controllers, giving a focused slice for testing repository queries and entity mappings.

By default it configures an in-memory embedded database (like H2) if available on the classpath and wraps each test in a transaction that's rolled back afterward, keeping tests isolated from each other. It also auto-configures TestEntityManager, a testing-friendly alternative to EntityManager for setting up test data with fine-grained control over flushing.

@DataJpaTest
class UserRepositoryTest {
    @Autowired private TestEntityManager entityManager;
    @Autowired private UserRepository userRepository;

    @Test
    void findByEmail_returnsUser() {
        entityManager.persist(new User("john@example.com"));
        Optional<User> found = userRepository.findByEmail("john@example.com");
        assertTrue(found.isPresent());
    }
}