assertNull(docMap.put("newKey", "newValue"));
        assertEquals("newValue", docMap.get("newKey"));

        assertEquals("newValue", docMap.put("newKey", "updatedValue"));
        assertEquals("updatedValue", docMap.get("newKey"));

        assertNull(docMap.get("nonexistent"));
    }

    public void test_remove() {
        Map<String, Object> parentMap = new HashMap<>();