assertEquals("ja", languageHelper.getSupportedLanguage("ja"));
        assertEquals("en", languageHelper.getSupportedLanguage("en"));
    }

    public void test_updateDocument_emptyLangFields() {
        languageHelper.langFields = new String[] {};

        Map<String, Object> doc = new HashMap<>();
        doc.put("lang", "ja");
        doc.put("title", "タイトル");