Oh. So it is less about I/O vs no-I/O and more about push parsing vs pull parsing. Because testing with a reader and writer interface lets you test errors too,

Oh. So it is less about I/O vs no-I/O and more about push parsing vs pull parsing. Because testing with a reader and writer interface lets you test errors too, but now you are talking about error recovery strategies (pull has to pass through or have smarts, push can know nothing). I agree in many cases push has the advantages being discussed. I just wouldn't have called it no-I/O since that doesn't really have the right connotation.