public void InitUpdatesIndex()
        {
            var store = MakeStore(2);

            store.Init(BasicUser, DataSet1, true);
            store.Init(OtherUser, DataSet2, true);

            var index = _persistentStore.InspectUserIndex(BasicMobileKey);

            Assert.Equal(
                ImmutableList.Create(Base64.UrlSafeSha256Hash(BasicUser.Key), Base64.UrlSafeSha256Hash(OtherUser.Key)),
                index.Data.Select(e => e.UserId).ToImmutableList()
                );
        }