Back in hs in the 00s my math teacher had a rule that you could use any program on your calculator if you wrote it yourself. She checked it by giving you a unique code and in the program it had to respond with your name.

I wrote a program each week to basically do the test. But I also wrote a wrapper which modified each program for any given code and name. It connected to the calculator, modified the program, copied program to calculator. I sold access to the program for 5 dollars per week.