@Test
  public void shouldClearSetAndThenMergeACustomer() throws Exception {

    Customer03 customer = new Customer03("Antony", "Balla", "*****@*****.**");

    // Persist the object
    tx.begin();
    em.persist(customer);
    tx.commit();
    assertTrue(em.contains(customer));

    em.clear();
    assertFalse(em.contains(customer));

    tx.begin();
    customer = em.merge(customer);
    customer.setFirstName("William");
    tx.commit();

    em.clear();
    assertFalse(em.contains(customer));

    customer = em.find(Customer03.class, customer.getId());
    assertEquals(customer.getFirstName(), "William");
    assertTrue(em.contains(customer));
  }
  @Test // Listing 4-14
  public void shouldPersistACustomerAndThenRefreshIt() throws Exception {

    Customer03 customer = new Customer03("Antony", "Balla", "*****@*****.**");
    Address03 address = new Address03("Ritherdon Rd", "London", "8QE", "UK");
    customer.setAddress(address);

    // Persist the object
    tx.begin();
    em.persist(customer);
    em.persist(address);
    tx.commit();

    assertNotNull(customer.getId());
    assertNotNull(address.getId());

    customer = em.find(Customer03.class, customer.getId());
    assertNotNull(customer);
    assertEquals(customer.getFirstName(), "Antony");

    customer.setFirstName("New first name");
    assertEquals(customer.getFirstName(), "New first name");

    em.refresh(customer);
    assertEquals(customer.getFirstName(), "Antony");
  }
  @Test // Listing 4-18
  public void shouldUpdateACustomer() throws Exception {

    Customer03 customer = new Customer03("Antony", "Balla", "*****@*****.**");

    // Persist the object
    tx.begin();
    em.persist(customer);

    assertNotNull(customer.getId());
    assertEquals(customer.getFirstName(), "Antony");

    customer.setFirstName("Williman");
    assertEquals(customer.getFirstName(), "Williman");

    tx.commit();
  }