how people do unit testing

A graduate student finished his thesis which was a networked terminal handler and asked me to test it.

I walked over to a logged out terminal, thought about it a bit and typed 3 charcters which happen to be a special case and crashed the entire timesharing system. I made the character position go negative,
 
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402DF855

Joined Feb 9, 2013
271
So you implement all the registers as of a real physical device and memory spaces, that is pretty cool! Do you have something to simulate the IOs as well?
Yes. For example my simulation will detect transmission on a UART (directly or via DMA) and write the results to the screen; and I can have it detect my keystrokes and put the characters into the UART receive register. Also, I can toggle some digital inputs to simulate external events. Obviously implementing all of the features of this processor (Cortex A5) would take a lifetime. Timer peripherals are fairly easy to implement and are often required for sequencing code execution, i.e. RTOS functions.
 
Way back when, and I don't know if it was before of after this incident a friend and I implemented "scope rubouts" e.g. VT100 CRT Terminal, on a timeshsring system called RSTS-11 on a PDP-11. He did the coding and I came up with the algorithm. Our employer had a full source code license. A soft <tab> was every 8 characters, I believe. This was an independent exercise.

The terminal was a hardcopy terminal called an LA36 that I typed the sequence on. The author of the networked handler was nearby.

Not sure, but I think the network protocol was DDCMP. See https://en.wikipedia.org/wiki/Digital_Data_Communications_Message_Protocol
 
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