Too many people have no idea what the difference between trial and testing is.

Trial is "smoke testing" wherein you look to see if it "works" at all. This is refined until one finally reaches the stage at which he's willing to tell the boss that it works perfectly and he'll bet his pay, his job, and the life of his first-born on it.

After that, a series of rigorous tests can be designed to verify that the device behaves exactly as it should under all circumstances occurring under "normal" operation and also how it is designed to behave under "abnormal" circumstances, e.g brownout, HF noise on the power line, glass of water poured on the enclosure, nuclear strike, whatever. Any deviation from design specification should be documented and remedied, before the first unit is shipped. A reasonable (1% ..10%) sample of all outgoing units should be similarly tested to ensure they are still meeting quality standards.

RE