@Test(expected = ValidationException.class)
  public void shouldNotCreateATweetBecauseLoginNull() {
    String login = null;
    String content = "content";

    Tweet tweet = new Tweet();
    tweet.setContent(content);
    tweet.setLogin(login);

    tweetRepository.createTweet(login, content);
  }
  @Test(expected = ConstraintViolationException.class)
  public void shouldNotCreateATweetBecauseContentEmpty() {
    String login = "******";
    String content = "";

    Tweet tweet = new Tweet();
    tweet.setContent(content);
    tweet.setLogin(login);

    tweetRepository.createTweet(login, content);
  }
  @Test
  public void shouldCreateATweet() {
    String login = "******";
    String content = "content";

    Tweet tweet = new Tweet();
    tweet.setContent(content);
    tweet.setLogin(login);

    assertThat(tweetRepository.createTweet(login, content), notNullValue());
  }