mod from_hex {     mod valid {        use git_hash::ObjectId;         #[test]        fn twenty_hex_chars_lowercase() {            assert!(ObjectId::from_hex(b"1234567890abcdefaaaaaaaaaaaaaaaaaaaaaaaa").is_ok());        }         #[test]        fn twenty_hex_chars_uppercase() {            assert!(ObjectId::from_hex(b"1234567890ABCDEFAAAAAAAAAAAAAAAAAAAAAAAA").is_ok());        }    }     mod invalid {        use git_hash::{decode, ObjectId};         #[test]        fn non_hex_characters() {            assert!(matches!(                ObjectId::from_hex(b"zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz").unwrap_err(),                decode::Error::Invalid { index: 0, c: 'z' }            ));        }         #[test]        fn too_short() {            assert!(matches!(                ObjectId::from_hex(b"abcd").unwrap_err(),                decode::Error::InvalidHexEncodingLength(4)            ));        }        #[test]        fn too_long() {            assert!(matches!(                ObjectId::from_hex(b"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaf").unwrap_err(),                decode::Error::InvalidHexEncodingLength(41)            ));        }    }}