@Test
  public void メッセージをクリアできる() {
    Messages msgs1 = new Messages(MessageType.ERROR);
    msgs1.add(new Message("CREATE_MESSAGE_TEST#001"));

    Messages msgs2 = new Messages(MessageType.ERROR);
    msgs2.add(new Message("CREATE_MESSAGE_TEST#002"));

    msgs1.add(msgs2);

    List<String> messegeList = msgs1.getMessageList();
    assertThat(messegeList.size(), is(2));

    msgs1.clear();
    assertThat(msgs1.isEmpty(), is(true));
  }