Writing Test Code

• spring-boot-starter-test: Key Testing Annotations
• JUnit 5
• Test classes should be placed under the src/test/java directory so that testing tools can automatically detect and run them.

Isolating tests

@SpringBootTest
@Transactional
class TransactionalTest {
 
    @Autowired
    private UserRepository userRepository;
 
    @Test
    void createUser() {
        User user = new User("testuser", "test@example.com");
        userRepository.save(user);
        // Automatically rolled back after test completes
    }
 
    @Test
    void getUser() {
        // given
        User user = new User("testuser", "test@example.com");
        User savedUser = userRepository.save(user);
 
        // when
        Optional<User> findUser = userRepository.findById(savedUser.getId());
 
        // then
        // findUser.get().getUsername().equals(savedUser.getUsername()) -> true expected
        // but result might be false if not handled properly
    }
}

• Each method annotated with @Test is run individually and independently by the test framework
  • each method runs inside its own transaction, which is automatically rolled back after the method finishes
  • Changes made in one test method do not affect other test methods.
  • The database state is reset after each test method, keeping tests isolated.
• Adding @Commit commits the transaction instead of rolling back.
  • Transaction behavior can vary based on propagation level.
• When used with JPA, pay attention to flush timing and persistence context management.
• @SpringBootTest
  • loads the entire application context, which can be slow.
  • Use it only when necessary, and prefer slice tests like @WebMvcTest or @DataJpaTest for faster, more focused testing.