Question about Specification about data-encoding HOT 6 CLOSED

#[test]
    fn check_unsigned_int()
    {
        // Examples come from RFC8949, Appendix A
        let var = 
        [
            ( 0_u64, "00" ),
            ( 1, "01" ),
            ( 10, "0a"),
            ( 23, "17"),
            ( 24, "1818"),
            ( 25, "1819"),
            ( 100, "1864" ),
            ( 1000, "1903e8"),
            ( 1000000, "1a000f4240"),
            ( 1000000000000, "1b000000e8d4a51000"),
            ( 18446744073709551615, "1bffffffffffffffff" ),
        ];

        validate_result( var )
    }
    
     fn validate_result<T : Cbor>(value : impl IntoIterator<Item = (T, &'static str)>)
    {
        for ( i, expected ) in value
        {
            let mut buf = Vec::new();

            i.encode(&mut buf).expect(&format!( "Failed to write buffer for {}", i));

            let hex = data_encoding::HEXLOWER.encode( &buf );

            assert_eq!( &hex, expected );
        }
    }