You need to perform the following steps to complete this recipe:

1. First, we need to create our persistence unit (at persistence.xml):

    <persistence-unit name="ch02-jta-pu" transaction-type="JTA">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        
        <jta-data-source>userDb</jta-data-source>
        <non-jta-data-source>userDbNonJta</non-jta-data-source>
        
        <exclude-unlisted-classes>false</exclude-unlisted-classes>

        <properties>
            <property name="javax.persistence.schema-
             generation.database.action" 
             value="create"/>
        </properties>
    </persistence-unit>

2. Then, we need to create a User class as an entity (@Entity):

@Entity
public class User implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    
    private String name;
    private String email;

    protected User() {
    } 
    
    public User(Long id, String name, String email) {
        this.id = id;
        this.name = name;
        this.email = email;
    }

    //DO NOT FORGET TO IMPLEMENT THE GETTERS AND SETTERS
}

3. We also need a Jakarta Enterprise Bean (formerly EJB) to perform the operations over the User entity:

@Stateful
public class UserBean {

    @PersistenceContext(unitName = "ch02-jta-pu", 
    type = PersistenceContextType.EXTENDED)
    private EntityManager em;
    
    public void add(User user){
        em.persist(user);
    }
    
    public void update(User user){
        em.merge(user);
    }
    
    public void remove(User user){
        em.remove(user);
    }
    
    public User findById(Long id){
        return em.find(User.class, id);
    }
}

4. Then, we need to create our unit test:

public class Ch02JtaTest {
    
    private EJBContainer ejbContainer;
    
    @EJB
    private UserBean userBean;
    
    public Ch02JtaTest() {
    }
    
    @Before
    public void setUp() throws NamingException {
        Properties p = new Properties();
        p.put("userDb", "new://Resource?type=DataSource");
        p.put("userDb.JdbcDriver", "org.hsqldb.jdbcDriver");
        p.put("userDb.JdbcUrl", "jdbc:hsqldb:mem:userdatabase");

        ejbContainer = EJBContainer.createEJBContainer(p);
        ejbContainer.getContext().bind("inject", this);
    }
    
    @After
    public void tearDown() {
        ejbContainer.close();
    }
    
    @Test
    public void validTransaction() throws Exception{
        User user = new User(null, "Elder Moraes", 
                             "[email protected]");
        
        userBean.add(user);
        user.setName("John Doe");
        userBean.update(user);
        
        User userDb = userBean.findById(1L);
        assertEquals(userDb.getName(), "John Doe");
        
    }
    
}