2 Corinthians 13:5

Unless indeed ye be reprobate

(ε μητ αδοκιμο εστε). Paul challenged his opposers in Corinth to try (πειραζετε) themselves, to test (δοκιμαζετε) themselves, whether they were "in the faith" (εν τη πιστε), a much more vital matter for them than trying to prove Paul a heretic. Such tests can be made, unless, alas, they are "reprobate" (αδοκιμο, the very adjective that Paul held up before himself as a dreadful outcome to be avoided, 1 Corinthians 9:27).