Any tank can leak at any time, but it's far more unlikely with a drop in coil setup. At least most of the time. The idea of "testing it' is not a bad one. I don't have any leaky tanks at the moment (including RTAs). I've never taken a drop in coil tank out of the house and had it leak though, unless something were to be drastically wrong (which I usually encounter before taking it out of the house). My mods get turned off and then float around in my purse with anything else in there. I'm pretty confident in my tanks these days... Unless something has side fill or something, vapes should not need to remain vertical in order to not leak.
Anna