assertTrue("Should contain all keys", Arrays.asList(keys).contains("b_key"));
        assertTrue("Should contain all keys", Arrays.asList(keys).contains("c_key"));
    }

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

        docMap.put("lang", "fr");