@Override
    public Set<String> keySet() {
        return new HashSet<>(lowerKeyToOriginMap.values());
    }
@Test
    void keySet() {
        Set<String> keySet = new HashSet<>();
        keySet.add("Key");
        keySet.add("Key2");
        Assertions.assertEquals(keySet, lowerCaseLinkHashMap.keySet());
    }