@Override
  public String getWelcomeMessage(User user) {
    if (UserGroup.isPaid(user)) {
      return "You're amazing " + user + ". Thanks for paying for this awesome software.";
    }

    return "I suppose you can use this software.";
  }
@Test
  void testGetWelcomeMessageForPaidUser() {
    final var welcomeMessage = service.getWelcomeMessage(paidUser);
    final var expected = "You're amazing Jamie Coder. Thanks for paying for this awesome software.";
    assertEquals(expected, welcomeMessage);
  }