public async Task WriteFile()
 {
     var fs = new FileAppendOnlyStoreAsync(new FileAppendOnlyStoreAsync.Options(File) { FileStream = s => Path.Combine(this.File, s + ".dat") });
     var es = new EventStoreAsync(fs);
     
     var id = new GuidId(Guid.NewGuid());
     await es.AppendToStream(id, 0, new List<IEvent>() {new MyNewEventEvent(id.ToString(), Guid.NewGuid(), DateTime.UtcNow)});
 }