mod lookup_ref_delta_objects {    use git_hash::ObjectId;    use git_pack::data::{entry::Header, input, input::LookupRefDeltaObjectsIter};     use crate::pack::hex_to_id;     const D_A: &[u8] = b"a";    const D_B: &[u8] = b"bb";    const D_C: &[u8] = b"ccc";    const D_D: &[u8] = b"dddd";     fn base() -> Header {        Header::Blob    }    fn delta_ofs(offset: u64) -> Header {        Header::OfsDelta { base_distance: offset }    }    fn delta_ref(id: ObjectId) -> Header {        Header::RefDelta { base_id: id }    }     fn extract_delta_offset(header: Header) -> u64 {        match header {            Header::OfsDelta { base_distance } => base_distance,            _ => unreachable!("this is supposed to be an offset header, was {:?}", header),        }    }     fn entry(header: Header, data: &'static [u8]) -> input::Entry {        let obj = git_object::Data {            kind: header.as_kind().unwrap_or(git_object::Kind::Blob),            data,        };        let mut entry = input::Entry::from_data_obj(&obj, 0).expect("valid object");        entry.header = header;        entry.header_size = header.size(data.len() as u64) as u16;        entry    }     fn compute_offsets(mut entries: Vec<input::Entry>) -> Vec<input::Entry> {        let mut offset = 0;        for entry in &mut entries {            entry.pack_offset = offset;            offset += entry.bytes_in_pack();        }        entries    }     fn validate_pack_offsets(entries: &[input::Entry]) {        let mut offset = 0;        for (eid, entry) in entries.iter().enumerate() {            assert_eq!(entry.pack_offset, offset, "invalid pack offset for entry {}", eid);            offset += entry.bytes_in_pack();        }    }     fn into_results_iter(        entries: Vec<input::Entry>,    ) -> impl ExactSizeIterator<Item = Result<input::Entry, input::Error>> {        entries.into_iter().map(Ok)    }     #[test]    fn only_ref_deltas_are_handled() -> crate::Result {        let input = compute_offsets(vec![entry(base(), D_A), entry(delta_ofs(100), D_B)]);        let expected = input.clone();        let actual =            LookupRefDeltaObjectsIter::new(into_results_iter(input), |_, _| unreachable!("not going to be called"))                .collect::<Result<Vec<_>, _>>()?;        assert_eq!(actual, expected, "it won't change the input at all");        validate_pack_offsets(&actual);        Ok(())    }     #[test]    fn ref_deltas_have_their_base_injected_if_not_done_before_and_all_future_entries_are_offset() {        let first_id = hex_to_id("0000000000000000000000000000000000000001");        let second_id = hex_to_id("0000000000000000000000000000000000000002");        let first = entry(delta_ref(first_id), D_A);         let inserted_data = D_D;        let mut inserted = entry(base(), inserted_data);        let second = entry(delta_ref(second_id), D_B);        let third_entry = entry(delta_ofs(second.bytes_in_pack()), D_C);        let fourth_entry = entry(delta_ofs(third_entry.bytes_in_pack()), D_D);        let fifth = entry(delta_ref(second_id), D_A);        let input = compute_offsets(vec![first.clone(), second, third_entry, fourth_entry, fifth]);         let mut calls = 0;        let input_entries = into_results_iter(input);        let actual_size = input_entries.size_hint();        let iter = LookupRefDeltaObjectsIter::new(input_entries, |_oid, buf| {            calls += 1;            buf.resize(inserted_data.len(), 0);            buf.copy_from_slice(inserted_data);            Some(git_object::Data {                kind: git_object::Kind::Blob,                data: buf.as_slice(),            })        });        assert_eq!(iter.size_hint(), (actual_size.0, actual_size.1.map(|s| s * 2)),                  "size hints are estimated and the upper bound reflects the worst-case scenario for the amount of possible objects");        let actual = iter.collect::<Result<Vec<_>, _>>().unwrap();         assert_eq!(calls, 2, "there is only two objects to insert");        assert_eq!(actual.len(), 7, "two object was inserted");         assert_eq!(&actual[0], &inserted, "first object is inserted one");         let altered = &actual[1];        assert_eq!(            extract_delta_offset(altered.header),            inserted.bytes_in_pack(),            "former first entry is now an offset delta pointing at the item before"        );         inserted.pack_offset = inserted.bytes_in_pack() + altered.bytes_in_pack();        assert_eq!(&actual[2], &inserted, "third object is a newly inserted one, too");         let altered = &actual[3];        assert_eq!(            extract_delta_offset(altered.header),            inserted.bytes_in_pack(),            "former second entry is now an offset delta pointing at the inserted item before"        );         let third = &actual[4];        assert_eq!(            extract_delta_offset(third.header),            altered.bytes_in_pack(),            "delta offset was adjusted to deal with change in size of predecessor(s)"        );        let fourth = &actual[5];        assert_eq!(            extract_delta_offset(fourth.header),            third.bytes_in_pack(),            "the fourth header base distance was adjusted accordingly"        );         let fifth = &actual[6];        assert_eq!(            fifth.pack_offset - extract_delta_offset(fifth.header),            actual[2].pack_offset,            "the fifth entry points exactly to the second inserted object, as objects are inserted only once"        );         validate_pack_offsets(&actual);    }     #[test]    fn lookup_errors_trigger_a_fuse_and_stop_iteration() {        let input = vec![entry(delta_ref(git_hash::Kind::Sha1.null()), D_A), entry(base(), D_B)];        let mut calls = 0;        let mut result = LookupRefDeltaObjectsIter::new(into_results_iter(input), |_, _| {            calls += 1;            None        })        .collect::<Vec<_>>();        assert_eq!(calls, 1, "it tries to lookup the object");        assert_eq!(result.len(), 1, "the error stops iteration");        assert!(matches!(            result.pop().expect("one"),            Err(input::Error::NotFound {                object_id            }) if object_id == git_hash::Kind::Sha1.null()        ))    }     #[test]    fn inner_errors_are_passed_on() {        let input = vec![            Ok(entry(base(), D_A)),            Err(input::Error::NotFound {                object_id: git_hash::Kind::Sha1.null(),            }),            Ok(entry(base(), D_B)),        ];        let expected = vec![            Ok(entry(base(), D_A)),            Err(input::Error::NotFound {                object_id: git_hash::Kind::Sha1.null(),            }),            Ok(entry(base(), D_B)),        ];        let actual = LookupRefDeltaObjectsIter::new(input.into_iter(), |_, _| unreachable!("wont be called"))            .collect::<Vec<_>>();        for (actual, expected) in actual.into_iter().zip(expected.into_iter()) {            assert_eq!(format!("{:?}", actual), format!("{:?}", expected));        }    }}