public class MessageSender {
  private Bot bot;
  private UserDirectory userDirectory;
  private MessageRepository repository;  
  private EmailSender emailSender; <--- MessageSender 클래스에 새로운 의존성을 추가한다.    
  private UserPreferences userPrefs; <--- MessageSender 클래스에 새로운 의존성을 추가한다.
  public MessageSender(Bot bot,
   UserDirectory userDirectory,
   MessageRepository repository,
   EmailSender emailSender,
   UserPreferences userPrefs) {
    this.bot = bot;
    this.userDirectory = userDirectory;
    this.repository = repository;