Test: a state index's long changes block reads back whole and in order 2cd6bf89adb4

    /// A changes block of thousands comes back whole and in order, and a

    /// truncated one is refused (oxygen#94).

    #[test]

    fn a_long_changes_block_decodes_in_order() {

        use crate::flat::Writer;

        let metas: Vec<(ChangeHash, ChangeMeta)> = (0..5000u32)

            .map(|i| {

                let mut h = [0u8; 32];

                h[..4].copy_from_slice(&i.to_le_bytes());

                let meta = ChangeMeta {

                    change_id: crate::ids::ChangeId([i as u8; 16]),

                    deps: (0..i % 3).map(|d| ObjectRef([d as u8; 32])).collect(),

                    author: ObjectRef([7; 32]),

                    hlc: Hlc {

                        wall_ms: 1_000_000 - i as u64,

                        logical: i,

                    },

                    message: "x".repeat((i % 50) as usize),

                    kind: ChangeKind::Normal,

                };

                (ObjectRef(h), meta)

            })

            .collect();

        let mut w = Writer::default();

        w.fixed(State::INDEX_MAGIC);

        w.count(metas.len());

        for (h, m) in &metas {

            w.object(h);

            m.write_flat(&mut w);

        }

        assert_eq!(State::read_index_changes_listed(&w.0).unwrap(), metas);

        let mut cut = w.0.clone();

        cut.pop();

        assert!(

            State::read_index_changes_listed(&cut).is_err(),

            "a truncated block is refused"

        );

    }