assertEquals(1, entrySet.size());

        String[] keys = entrySet.stream().map(Map.Entry::getKey).toArray(String[]::new);
        assertEquals("lang", keys[0]);
    }

    public void test_entrySet_multiple_lang_keys() {
        Map<String, Object> parentMap = new LinkedHashMap<>();
        DocMap docMap = new DocMap(parentMap);

        docMap.put("lang", "ja");
        docMap.put("other", "value");