@Entity // Add Entity annotation to mark the class as an entity
public class EmployeeEntity {
    // Class definition
}

public class CustomJpaDaoIntegrationTest {

    // EntityManagerFactory and EntityManager for custom persistence unit
    private final EntityManagerFactory customEmf = Persistence.createEntityManagerFactory("custom-pu-test");
    private final EntityManager customEntityManager = customEmf.createEntityManager();

    // Setup method to delete all employees before each test
    @Before
    public void setup() {
        deleteAllEmployees();
    }

    // Method to delete all employees from the database
    private void deleteAllEmployees() {
        // Begin transaction
        customEntityManager.getTransaction().begin();
        // Execute native SQL query to delete all employees
        customEntityManager.createNativeQuery("DELETE from EmployeeEntity").executeUpdate();
        // Commit transaction
        customEntityManager.getTransaction().commit();
    }

    // Method to save an employee entity to the database
    public void save(EmployeeEntity entity) {
        // Begin transaction
        customEntityManager.getTransaction().begin();
        // Persist the entity
        customEntityManager.persist(entity);
        // Commit transaction
        customEntityManager.getTransaction().commit();
    }

    // Method to update an employee entity in the database
    public void update(EmployeeEntity entity) {
        // Begin transaction
        customEntityManager.getTransaction().begin();
        // Merge the entity
        customEntityManager.merge(entity);
        // Commit transaction
        customEntityManager.getTransaction().commit();
    }

    // Method to delete an employee from the database by employee ID
    public void delete(Long employeeId) {
        // Begin transaction
        customEntityManager.getTransaction().begin();
        // Find and remove the entity by ID
        customEntityManager.remove(customEntityManager.find(EmployeeEntity.class, employeeId));
        // Commit transaction
        customEntityManager.getTransaction().commit();
    }

    // Method to update entities using CriteriaUpdate and return the number of updated records
    public int update(CriteriaUpdate<EmployeeEntity> criteriaUpdate) {
        // Begin transaction
        customEntityManager.getTransaction().begin();
        // Execute the CriteriaUpdate query and get the result
        int result = customEntityManager.createQuery(criteriaUpdate).executeUpdate();
        // Commit transaction
        customEntityManager.getTransaction().commit();
        // Clear the entity manager
        customEntityManager.clear();
        // Return the number of updated records
        return result;
    }
}

// Configuration class for custom Spring Data JPA settings
@Configuration
@EnableTransactionManagement
@EnableJpaRepositories(basePackageClasses = CustomRepository.class)
public class CustomSpringDataJpaConfig {

    // Bean definition for custom entity manager factory
    @Bean
    public LocalContainerEntityManagerFactoryBean customEntityManagerFactory(DataSource customDataSource) {
        // Creating entity manager factory bean
        LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();
        // Setting custom data source
        em.setDataSource(customDataSource);
        // Scanning packages for entity classes
        em.setPackagesToScan(EmployeeEntity.class.getPackage().getName());

        // Configuring JPA vendor adapter
        JpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
        em.setJpaVendorAdapter(vendorAdapter);

        // Setting Hibernate properties
        Properties properties = new Properties();
        properties.setProperty("hibernate.hbm2ddl.auto", "create-drop");
        properties.setProperty("hibernate.dialect", "org.hibernate.dialect.H2Dialect");
        em.setJpaProperties(properties);

        return em;
    }

    // Bean definition for custom transaction manager
    @Bean
    public PlatformTransactionManager customTransactionManager(LocalContainerEntityManagerFactoryBean customEntityManagerFactoryBean) {
        // Creating custom transaction manager
        JpaTransactionManager transactionManager = new JpaTransactionManager();
        transactionManager.setEntityManagerFactory(customEntityManagerFactoryBean.getObject());
        return transactionManager;
    }

    // Bean definition for custom data source
    @Bean
    public DataSource customDataSource() {
        return DataSourceBuilder.create()
          .driverClassName("org.h2.Driver")
          .username("customuser")
          .password("custompassword")
          .build();
    }

    // Bean definition for custom JPA query factory
    @Bean
    public JPAQueryFactory customJpaQueryFactory(EntityManager entityManager) {
        return new JPAQueryFactory(entityManager);
    }
}