@Override
    public boolean containsKey(Object key) {
        return map1.containsKey(key) || map2.containsKey(key);
    }
@Test
    public void testContainsKey() {
        Map<String, String> map1 = new HashMap<>();
        map1.put("key1", "value1");

        Map<String, String> map2 = new HashMap<>();
        map2.put("key2", "value2");

        Map<String, String> aggregatingMap = AggregatingMap.aggregate(map1, map2);
        assertTrue(aggregatingMap.containsKey("key1"));
        assertTrue(aggregatingMap.containsKey("key2"));
        assertFalse(aggregatingMap.containsKey("key3"));
    }