public void Set_take_snapshot()
        {
            SnapshotableDb db = new SnapshotableDb(new MemDb());

            db.Set(_hash1, _bytes1);
            Assert.AreEqual(0, db.TakeSnapshot());
        }
        public void Initial_take_snapshot()
        {
            SnapshotableDb db = new SnapshotableDb(new MemDb());

            Assert.AreEqual(-1, db.TakeSnapshot());
        }