#[cfg(test)]
mod tests {
    use crate::gray_code::gray_code;

    #[test]
    fn digits() {
        assert_eq!(gray_code(0), 0);
        assert_eq!(gray_code(1), 1);
        assert_eq!(gray_code(2), 3);
        assert_eq!(gray_code(3), 2);
        assert_eq!(gray_code(4), 6);
        assert_eq!(gray_code(5), 7);
        assert_eq!(gray_code(6), 5);
        assert_eq!(gray_code(7), 4);
        assert_eq!(gray_code(8), 12);
        assert_eq!(gray_code(9), 13);
    }

    #[test]
    fn msb_u32() {
        assert_eq!(gray_code(3_000_000_000), 3_954_733_312);
        assert_eq!(gray_code(2_147_483_648), 3_221_225_472);
		assert_eq!(gray_code(4_294_967_295), 2_147_483_648);
    }
}