w08 7/15, p. 28
"To 'test whether we are in the faith,' we have to measure our conduct in the light of what we learn from the Bible. To 'prove what we ourselves are,' we have to evaluate the level of our spirituality, including the sharpness of our "perceptive powers" and the extent of our works of faith. (Heb. 5:14; Jas. 1:22-25) By applying Paul's sound advice, we can keep on walking in the way of the truth."
I think this Watchtower (based on the Bible) perfectly answers your questions.
