mod prefix {    mod cmp_oid {        use std::cmp::Ordering;         use git_testtools::hex_to_id;         #[test]        fn it_detects_inequality() {            let prefix = git_hash::Prefix::new(hex_to_id("b920bbb055e1efb9080592a409d3975738b6efb3"), 7).unwrap();            assert_eq!(                prefix.cmp_oid(&hex_to_id("a920bbb055e1efb9080592a409d3975738b6efb3")),                Ordering::Greater            );            assert_eq!(                prefix.cmp_oid(&hex_to_id("b920bbf055e1efb9080592a409d3975738b6efb3")),                Ordering::Less            );            assert_eq!(prefix.to_string(), "b920bbb");        }         #[test]        fn it_detects_equality() {            let id = hex_to_id("a920bbb055e1efb9080592a409d3975738b6efb3");            let prefix = git_hash::Prefix::new(id, 6).unwrap();            assert_eq!(prefix.cmp_oid(&id), Ordering::Equal);            assert_eq!(                prefix.cmp_oid(&hex_to_id("a920bbffffffffffffffffffffffffffffffffff")),                Ordering::Equal            );            assert_eq!(prefix.to_string(), "a920bb");        }    }    mod new {        use std::cmp::Ordering;         use git_hash::{Kind, ObjectId};        use git_testtools::hex_to_id;         #[test]        fn various_valid_inputs() {            let oid_hex = "abcdefabcdefabcdefabcdefabcdefabcdefabcd";            let oid = hex_to_id(oid_hex);             for hex_len in 4..oid.kind().len_in_hex() {                let mut expected = String::from(&oid_hex[..hex_len]);                let num_of_zeros = oid.kind().len_in_hex() - hex_len;                expected.extend(std::iter::repeat('0').take(num_of_zeros));                let prefix = git_hash::Prefix::new(oid, hex_len).unwrap();                assert_eq!(prefix.as_oid().to_hex().to_string(), expected, "{}", hex_len);                assert_eq!(prefix.hex_len(), hex_len);                assert_eq!(prefix.cmp_oid(&oid), Ordering::Equal);            }        }         #[test]        fn errors_if_hex_len_is_longer_than_oid_len_in_hex() {            let kind = Kind::Sha1;            assert!(matches!(                git_hash::Prefix::new(ObjectId::null(kind), kind.len_in_hex() + 1),                Err(git_hash::prefix::Error::TooLong { .. })            ));        }         #[test]        fn errors_if_hex_len_is_too_short() {            let kind = Kind::Sha1;            assert!(matches!(                git_hash::Prefix::new(ObjectId::null(kind), 3),                Err(git_hash::prefix::Error::TooShort { .. })            ));        }    }     mod try_from {        use std::{cmp::Ordering, convert::TryFrom};         use git_hash::{prefix::from_hex::Error, Prefix};        use git_testtools::hex_to_id;         #[test]        fn id_8_chars() {            let oid_hex = "abcdefabcdefabcdefabcdefabcdefabcdefabcd";            let input = "abcdef";             let expected = hex_to_id(oid_hex);            let actual = Prefix::try_from(input).expect("No errors");            assert_eq!(actual.cmp_oid(&expected), Ordering::Equal);        }         #[test]        fn id_9_chars() {            let oid_hex = "abcdefabcdefabcdefabcdefabcdefabcdefabcd";            let input = "abcdefa";             let expected = hex_to_id(oid_hex);            let actual = Prefix::try_from(input).expect("No errors");            assert_eq!(actual.cmp_oid(&expected), Ordering::Equal);        }        #[test]        fn id_to_short() {            let input = "ab";            let expected = Error::TooShort { hex_len: 2 };            let actual = Prefix::try_from(input).unwrap_err();            assert_eq!(actual, expected);        }         #[test]        fn id_to_long() {            let input = "abcdefabcdefabcdefabcdefabcdefabcdefabcd123123123123123123";            let expected = Error::TooLong { hex_len: 58 };            let actual = Prefix::try_from(input).unwrap_err();            assert_eq!(actual, expected);        }         #[test]        fn invalid_chars() {            let input = "abcdfOsd";            let expected = Error::Invalid { c: 'O', index: 5 };            let actual = Prefix::try_from(input).unwrap_err();            assert_eq!(actual, expected);        }    }} mod short_hex {    #[test]    fn display_entire_range_sha1() {        let id_hex = "0123456789abcdef123456789abcdef123456789";        let id = git_hash::ObjectId::from_hex(id_hex.as_bytes()).expect("valid input");        for len in 0..=40 {            assert_eq!(id.to_hex_with_len(len).to_string(), id_hex[..len]);        }        assert_eq!(            id.to_hex_with_len(120).to_string(),            id_hex,            "values that are too long are truncated"        );    }}