@Test
void test() {

    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);
}