For any new discrete operation, I create logic and simulate/test all of the associated conditions in a PLC that is hanging on my office wall (development). Once I am confident that everything works as designed, I migrate the operation to the running system (deployment). Once it is there, then I usually have to do some amount of testing, but as it was tested during development confidence is high that everything works. Anything that is not tested is not certain to work when called on, no matter how simple it seems.
Brad Waybright
It's all okay as long as it's okay.