As a systems integrator, it is your job to make sure that assembly line and similar systems function flawlessly. The only way to make sure that your programming works is to literally try your best to break it. You have to think of any possible commands that an assembly line tech might input and see if any problems arise with your software. Assuring the quality of your software is the foundation of managing your risk as a systems integrator.
If a client comes back and claims that you delivered faulty software and sues you, it is important that you can back up your work by proving that you have an effective quality assurance testing program in place. Not only does having this process documented properly help you in the event of a lawsuit, it should help to prevent the lawsuits from ever occurring cause it will catch most, if not all of the potential problems that could exist with your final product.