@Test
  public void preventsDuplicateEmail() {

    Customer dave = repository.findByEmailAddress(new EmailAddress("*****@*****.**"));

    Customer anotherDave = new Customer("Dave", "Matthews");
    anotherDave.setEmailAddress(dave.getEmailAddress());

    repository.save(anotherDave);
  }
  @Test
  public void readsCustomerByEmail() {

    EmailAddress email = new EmailAddress("*****@*****.**");
    Customer alicia = new Customer("Alicia", "Keys");
    alicia.setEmailAddress(email);

    repository.save(alicia);

    Customer result = repository.findByEmailAddress(email);
    assertThat(result, is(alicia));
  }