[HeyLaughingBoy]

the original test specification was literally “plug the device into the USB port of [your] laptop, and type in this AVRDUDE command to load code

At the outfit I work for this is pretty much what they were doing for one of the products when I started. It wasn't that they didn't know better (they had other items in mass production); it was that the product used to be such a low volume that typing in CLI commands to program and test it was (almost) good enough.

I spent months automating that to the point of "plug cable into device and watch for Pass/Fail" indication on screen. Now that we're shipping thousands per month it make a huge difference :-)

Testing is a weird thing. The points you test are a function of what you expect may fail in manufacturing. No point in testing something that's extremely unlikely to fail, unless it's required by regulation.

e.g., FDA (Food & Drug Administration) Good Manufacturing Practices state that if you don't build something using a documented and repeatable process then you must test 100% of product coming off the line. If you have a tight manufacturing process, then you can decide what level of testing meets a good balance of safety and cost.

People spend their entire career as Test & Manufacturing engineers and it is quite a complex and interesting field.