Arduino program to test (you guessed it) cables with a Teensy LC. ADTPro serial cables, specifically.
Wire up connectors that accept the mates of both ends of a cable to pins on the Teensy, then ask it if the expected pins are connected—and ensure no connection exists where one shouldn't be, one pin at a time, checking against all possible pins on the other end.
To make the tester "universal" (for DIN5 and MiniDIN8 cables), I created whips for the different cable types
Cable recipes are from the ADTPro project: https://adtpro.com/connectionsserial.html