Cap K asks Does anyone have any reference for when it (prove meaning test) was first used?

The AHD isn't terribly specific here but it does say in its etymology for the word: Middle English proven, from Old French prover, from Latin probare, to test, from probus, good. which would suggest that it had the meaning test. We'll have to look it up in the OED to get the straight skinny and mine is at home.