@Override
    public boolean containsKey(Object o) {
        if (o instanceof String) {
            return targetMap.containsKey(((String) o).toLowerCase());
        }

        return false;
    }
@Test
    void containsKey() {
        Assertions.assertTrue(lowerCaseLinkHashMap.containsKey("key"));
        Assertions.assertTrue(lowerCaseLinkHashMap.containsKey("Key"));
        Assertions.assertTrue(lowerCaseLinkHashMap.containsKey("KEY"));
        Assertions.assertFalse(lowerCaseLinkHashMap.containsKey("test"));
        Assertions.assertFalse(lowerCaseLinkHashMap.containsKey(123));
    }