test_sync.py

    def test_wait_for_invalid_future_sync_token(self) -> None:
        """Like the previous test, except we give a token that has a stream
        position ahead of what is in the DB, i.e. its invalid and we shouldn't
        wait for the stream to advance (as it may never do so).

        This can happen due to older versions of Synapse giving out stream
        positions without persisting them in the DB, and so on restart the
        stream would get reset back to an older position.
        """
        user = self.register_user("alice", "password")

        # Create a token and arbitrarily advance one of the streams.
        current_token = self.hs.get_event_sources().get_current_token()
        since_token = current_token.copy_and_advance(
            StreamKeyType.PRESENCE, current_token.presence_key + 1
        )

        sync_d = defer.ensureDeferred(
            self.sync_handler.wait_for_sync_for_user(
                create_requester(user),
                generate_sync_config(user),
                sync_version=SyncVersion.SYNC_V2,
                request_key=generate_request_key(),
                since_token=since_token,
                timeout=0,
            )
        )

        # We should return without waiting for the presence stream to advance.
        self.get_success(sync_d)


def generate_sync_config(
    user_id: str,
    device_id: Optional[str] = "device_id",
    filter_collection: Optional[FilterCollection] = None,
) -> SyncConfig:
    """Generate a sync config (with a unique request key).

    Args:
        user_id: user who is syncing.
        device_id: device that is syncing. Defaults to "device_id".
        filter_collection: filter to apply. Defaults to the default filter (ie,
           return everything, with a default limit)
    """
    if filter_collection is None:
        filter_collection = Filtering(Mock()).DEFAULT_FILTER_COLLECTION

    return SyncConfig(
        user=UserID.from_string(user_id),
        filter_collection=filter_collection,
        is_guest=False,
        device_id=device_id,
    )