@Override
  public Optional<Language> find(String languageKey) {
    return Optional.ofNullable(languagesByKey.get(languageKey));
  }
@Test
  public void find_by_other_key_returns_absent() {
    LanguageRepositoryImpl languageRepository = new LanguageRepositoryImpl(SOME_LANGUAGE);
    Optional<Language> language = languageRepository.find(ANY_KEY);
    assertThat(language).isEmpty();
  }