    #[test]
    fn test_concat_cons_char_types_no_boundary() {
        let s = Sentence::from_tokenized("5").unwrap();
        let filter = KyteaWsConstFilter::new(CharacterType::Digit);
        let s = filter.filter(s);
        assert_eq!("5", s.to_tokenized_string().unwrap());
    }

    #[test]
    fn test_concat_cons_char_types() {
        let s = Sentence::from_tokenized("5 00 0").unwrap();
        let filter = KyteaWsConstFilter::new(CharacterType::Digit);