I tested different control schemes and thrust firing plans, added support for different types of thrusters, errors in sensor readings, atmospheric drag depending on altitude, weird anomalies in the earth's magnetic field, simulated bit flip events and hardware lockups (I left the internal watchdog out of the hardware lockups which is probably not realistic).
In an effort to stress test my simulator I ended up writing a genetic algorithm solver for thruster, magneto-torquer, and reaction wheel placement on arbitrary craft bodies with different mission plans and let it solve it.
I ended up designing a physical circuit board matching the simulator, flashing the board with the same code that was running in the simulator and it worked! I roughly made an approximate cube sat (10cm^3) (had a mechanical engineer friend design me a frame and manufacture it for me) with some small cold gas thrusters out of pressurized CO2 cartridges, controlled by solenoids, and placed by my genetic algorithm.
I dropped it off a cliff that was ~600ft high (best I could do for a "zero gravity" environment that was away from people). It was able to completely arrest its angular rotation before slamming into the ground which is better than I was expecting.