@DataJpaTest for repository testing in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the test execution result of this @DataJpaTest?

Consider this JUnit test using @DataJpaTest for a Spring Data JPA repository. What will be the test result?

JUnit

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
import static org.assertj.core.api.Assertions.assertThat;

@DataJpaTest
class UserRepositoryTest {

    @Autowired
    private UserRepository userRepository;

    @Test
    void testSaveAndFind() {
        User user = new User(null, "Alice");
        userRepository.save(user);
        User found = userRepository.findByName("Alice");
        assertThat(found).isNotNull();
        assertThat(found.getName()).isEqualTo("Alice");
    }
}

A Test passes because the user is saved and found correctly in the in-memory database.

B Test fails with NullPointerException because userRepository is not injected.

C Test fails with DataIntegrityViolationException due to missing @Transactional annotation.

D Test fails because @DataJpaTest disables repository beans by default.

💡 Hint

Remember that @DataJpaTest configures an in-memory database and injects repository beans automatically.

@DataJpaTest sets up an in-memory database and scans for JPA repositories. It injects the repository bean, so userRepository is available. The test saves a user and finds it by name, so assertions pass.

❓ assertion

intermediate

Which assertion correctly verifies the repository returns no users initially?

Given a UserRepository with method findAll(), which assertion correctly checks that the repository is empty before any save?

JUnit

import static org.junit.jupiter.api.Assertions.*;

List<User> users = userRepository.findAll();

A assertNotNull(users); assertEquals(0, users.size());

B assertEquals(null, users);

C assertTrue(users.isEmpty());

D assertFalse(users.isEmpty());

💡 Hint

Check if the list returned by findAll() contains any elements.

findAll() returns an empty list if no users exist. Using assertTrue(users.isEmpty()) directly checks that the list has no elements.

🔧 Debug

advanced

Why does this @DataJpaTest fail with NoSuchBeanDefinitionException?

This test fails with NoSuchBeanDefinitionException for UserRepository. What is the likely cause?

JUnit

@DataJpaTest
class UserRepositoryTest {

    @Autowired
    private UserRepository userRepository;

    @Test
    void testFind() {
        User user = userRepository.findByName("Bob");
        assertNull(user);
    }
}

A UserRepository interface is missing @Repository annotation.

B The test class is missing @SpringBootTest annotation to load the full context.

C The test method is missing @Transactional annotation.

D UserRepository is not in the same package or a subpackage of the test class, so it is not scanned.

💡 Hint

Check the package structure and component scanning rules of @DataJpaTest.

@DataJpaTest scans for JPA repositories only in the package of the test class and its subpackages. If UserRepository is outside this scope, it won't be found, causing NoSuchBeanDefinitionException.

🧠 Conceptual

advanced

What is the default database used by @DataJpaTest?

When running a test annotated with @DataJpaTest without any database configuration, which database is used by default?

A An embedded in-memory H2 database

B The production MySQL database configured in application.properties

C An embedded in-memory Derby database

D No database is used; repositories are mocked automatically

💡 Hint

Spring Boot auto-configures an embedded database for tests if available.

@DataJpaTest auto-configures an embedded in-memory H2 database by default if no other datasource is configured. It does not use production databases or mocks repositories.

❓ framework

expert

Which annotation combination ensures @DataJpaTest rolls back transactions after each test?

You want each test method in a @DataJpaTest class to run in a transaction that rolls back after the test completes. Which annotation setup achieves this?

A @DataJpaTest with @Commit to commit transactions after tests

B @DataJpaTest alone (default rollback behavior enabled)

C @DataJpaTest with @Transactional(propagation = Propagation.NOT_SUPPORTED)

D @DataJpaTest with @Rollback(false) to disable rollback

💡 Hint

Check the default transaction behavior of @DataJpaTest.

@DataJpaTest runs each test method in a transaction that rolls back by default after the test finishes. Adding @Transactional with NOT_SUPPORTED disables transactions, and @Commit or @Rollback(false) change rollback behavior.