public void enter(Wizard wizard) {
    LOGGER.info("{} enters the tower.", wizard);
  }
@Test
  void testEnter() {
    final var wizards = List.of(
        new Wizard("Gandalf"),
        new Wizard("Dumbledore"),
        new Wizard("Oz"),
        new Wizard("Merlin")
    );

    var tower = new IvoryTower();
    wizards.forEach(tower::enter);

    assertTrue(appender.logContains("Gandalf enters the tower."));
    assertTrue(appender.logContains("Dumbledore enters the tower."));
    assertTrue(appender.logContains("Oz enters the tower."));
    assertTrue(appender.logContains("Merlin enters the tower."));
    assertEquals(4, appender.getLogSize());
  }