“What does ‘test yourselves’ mean in 2 Corinthians 13:5?”
Self-assessments are notoriously hard to get right, even for Christians. As Jeremiah put it, “The heart is deceitful above all things, and desperately sick; who can understand it?” If our security in Christ depends on our ability to correctly analyze the state of our own belief, then we are bound to be perpetually short of the spiritual confidence necessary to live victoriously.
I think the key to properly understanding that passage is recognizing Paul intended “test yourselves” neither individually nor subjectively. Evidence to follow …