“Test yourselves to see if you re in the faith; examine yourselves! Or do you not recognize this about yourselves, that Jesus Christ is in you~unless indeed you fail the test?” 2 Corinthians 13:5
The grammar places great emphasis on the pronouns “yourselves” and “you”. Paul turned the tables on his accusers; instead of presuming to evaluate his apostleship, they needed to test the genuineness of their faith (cf. Jas. 2:14-26). He pointed out the incongruity of the Corinthians’ believing (as they did) that their faith was genuine and his apostleship false. Paul was their spiritual father (1 Co. 4:15); if his apostleship was counterfeit, so was their faith. The genuineness of their salvation was proof of the genuineness of his apostleship.
To fail the test is literally ‘not approved’. Here it referred to the absence of genuine saving faith.