Design for manufacturability
I'm just a noob in electronics, but I will do my best to think of some considerations:


Checking for each component's datasheet, that the ranges where the component work in are (well) within specifications (i.e. not more current/voltage than specified)
Endurance tests, probably with voltage/current close to the range, maybe even slightly above it. Although endurance tests are not done for more than hours/days probably (per test).
For safety (not related to 6 months) there are a lot of rules, depending per country. Manufacturers should apply these rules in their products.
Probably also 'misuse' by users is taken care of, like not accidentally using the device with an adapter reversed (by using diodes).
EMF tests or other tests with hash conditions, like noisy environments for motors/sensors/communication devices.