protected virtual CheckpointStrategy CreateCheckpointStrategy()
 {
     var result = new CheckpointStrategy.Builder();
     if (_source != null)
     {
         _source(result);
     }
     else
     {
         result.FromAll();
         result.AllEvents();
         result.SetEmitStateUpdated();
     }
     return result.Build(ProjectionConfig.GetTest());
 }