At work I can say: Те́стить(imperfect) → Проте́стить(perfect) → Проте́щенный(derived adjective) and coworkers will understand me.
Probably, grammatically more correct is протесщенныйпротеСЩенный or проте_стщ_енныйпротеСТЩенный, but it's hard to pronounce, in colloquial speech it shorten to single "щ".