source: class MessagingAppTest {
  
      private UserRepository userRepository;
      private MessageRepository messageRepository;
  
      @Test
      void test() {
  
target:         Iterable<User> users = userRepository.saveAll(
                  Stream.of("lola", "bola")
                        .map(name -> new User(null, name))
                        .collect(Collectors.toList()));
          log.info("saved: {}", users);
  
          Iterator<User> iterator = userRepository.findAll()
                                                  .iterator();
          User from = iterator.next();
          User to = iterator.next();
  
          Iterable<Message> messages = messageRepository.saveAll(
                  Stream.of("ololo", "trololo")
                        .map(body -> new Message(null, body, UserRef.of(from), UserRef.of(to)))
                        .collect(Collectors.toList()));
          log.info(messages);
      }
  
  }