Anything going into flight hardware gets tested in some very wired, sometimes, scenarios:
To 'Qualify' a part, let's say a small relay box, it could have to operate, at like, minus 65 degrees. (Farenheit).
Add in some (substantial) vibration, for, say, 2 hours on each 'axis'. For that, just for that, somebody in Engineering Dept will have to design / machine a 'plate' for mounting to the vibration table.
That table has a 'voice coil', something like a (large) diesel truck engine, in size and shape.
And don't forget heat: for that combination, you need an oven, for 'lowering down' over your part, mounting plate, and big vibration test table. So, during those tests, you get to learn about hotels / travel / late nights watching, from a folding chair. Yeah...:
Then it happens: a RELAY or something breaks, during third hour, of test...
Some of what I'm describing is 'environmental tolerance type, such as, also, salt spray, under-voltages, and EVEN HITTING WITH HAMMER !
There are, actual tests where QC folks give a crack with a 'special' moderately hard plastic head. Heck, there is even, I guess, an engineer somewhere, had to specify that (hammer).
A lot of that extra testing might be only for military goods, but testing I saw was commercial aircraft.
Some of those jobs don't have direct pc board design tasks, but you must be ready and understand issues clearly, and much to learn, while working.
If it's a career thing, not too bad a deal as you can use that salary money, to set up hobby lab etc.
Don't forget, option to take a course at night, while doing the Test Engineer gig.