mod ancestor {    use crate::hex_to_id;    use git_hash::ObjectId;    use git_odb::{linked::Db, pack, FindExt};    use git_traverse::commit;     fn db() -> crate::Result<Db> {        let dir = git_testtools::scripted_fixture_repo_read_only("make_traversal_repo_for_commits.sh")?;        let db = Db::at(dir.join(".git").join("objects"))?;        Ok(db)    }     fn new_iter(        tips: impl IntoIterator<Item = impl Into<ObjectId>>,    ) -> impl Iterator<Item = Result<ObjectId, commit::ancestors::Error>> {        let db = db().expect("db instantiation works as its definitely valid");        commit::Ancestors::new(tips, commit::ancestors::State::default(), move |oid, buf| {            db.find_existing_commit_iter(oid, buf, &mut pack::cache::Never).ok()        })    }     fn check_traversal_with_shared_reference(tips: &[&str], expected: &[&str]) -> crate::Result {        let tips: Vec<_> = tips.iter().copied().map(hex_to_id).collect();        let oids: Result<Vec<_>, _> = new_iter(tips.iter().cloned()).collect();        let expected: Vec<_> = tips            .into_iter()            .chain(expected.iter().map(|hex_id| hex_to_id(hex_id)))            .collect();        assert_eq!(oids?, expected);        Ok(())    }     #[test]    fn instantiate_with_arc() -> crate::Result {        let _ = new_iter(vec![git_hash::ObjectId::null_sha1()]);        Ok(())    }     #[test]    fn instantiate_with_box() -> crate::Result {        let _ = new_iter(vec![git_hash::ObjectId::null_sha1()]);        Ok(())    }     #[test]    fn linear_history_no_branch() -> crate::Result {        check_traversal_with_shared_reference(            &["9556057aee5abb06912922e9f26c46386a816822"],            &[                "17d78c64cef6c33a10a604573fd2c429e477fd63",                "9902e3c3e8f0c569b4ab295ddf473e6de763e1e7",                "134385f6d781b7e97062102c6a483440bfda2a03",            ],        )    }     #[test]    fn simple_branch_with_merge() -> crate::Result {        check_traversal_with_shared_reference(            &["01ec18a3ebf2855708ad3c9d244306bc1fae3e9b"],            &[                "efd9a841189668f1bab5b8ebade9cd0a1b139a37",                "ce2e8ffaa9608a26f7b21afc1db89cadb54fd353",                "9556057aee5abb06912922e9f26c46386a816822",                "9152eeee2328073cf23dcf8e90c949170b711659",                "17d78c64cef6c33a10a604573fd2c429e477fd63",                "9902e3c3e8f0c569b4ab295ddf473e6de763e1e7",                "134385f6d781b7e97062102c6a483440bfda2a03",            ],        )    }     #[test]    fn multiple_tips() -> crate::Result {        check_traversal_with_shared_reference(            &[                "01ec18a3ebf2855708ad3c9d244306bc1fae3e9b",                "9556057aee5abb06912922e9f26c46386a816822",            ],            &[                "efd9a841189668f1bab5b8ebade9cd0a1b139a37",                "ce2e8ffaa9608a26f7b21afc1db89cadb54fd353",                "17d78c64cef6c33a10a604573fd2c429e477fd63",                "9152eeee2328073cf23dcf8e90c949170b711659",                "9902e3c3e8f0c569b4ab295ddf473e6de763e1e7",                "134385f6d781b7e97062102c6a483440bfda2a03",            ],        )    }}