pub fn test_stop_processing(self) {
        let (stop_sender, stop_receiver) = mpsc::sync_channel(0);
        self.command_sender.send(Command::Stop(stop_sender)).ok();
        stop_receiver.recv().ok();
    }
Emulates stopping persisting updates; any updates afterwards will not actually be persisted.

This method should only be used in tests. It is blocking (waits until all previous persistence commands are processed).
core/lib/merkle_tree/src/storage/parallel.rs