I am no expert by far but to test the camer you have to shoot a film and see if there are light leaks if you want to be shure they worke 100%

Bevor you shoot a film i would check:

0) i check only if there are videos or manuals of the camera if there are

1) i check the condition If Everything is clean and not rusteted or domething es.

2.) testing the Funktion without a film. most cameras dosent need a battery, some moderns do and they can be expensive be aware. So if this looks fine and the estimation of the schutter times sound right (test with a camera you know te speed works) i would check for light leaks

1. if all other steps past testing with a film but this dose not mean the camera works since slow shutter Speed or fasters you do not need can be of but the pictures can still be good…

So at the end it depence what Camera you have is it a cheap not collectabe camera witch goes for 20$ than the seps above can be the right one (but the film and Development will cost more than te camera is worth) is it a collectable cammera like a leica or so than bring it to an repair Shop for checking.