If you wish to test the validity of your own powers, you must first study the koan on the death of Nan-ch'uan.
A long time ago San-sheng had the head monk Hsiu go to the Zen Master Tsen of Ch'ang-sha and ask him: "What happened to Nan-ch'uan after he passe[d] away?"
Ch'ang-sha replied: "When Shih-t'ou became a novice monk he was seen by the Sixth Patriarch."
Hsiu replied: "I didn't ask you about when Shih-t'ou became a novice monk; I asked you what happened to Nan-ch'uan after he passed away."
Ch'ang-sha replied: "If I were you I would let Nan-ch'uan worry about it himself."
Hsiu replied: "Even though you had a thousand-foot winter pine, there is no bamboo shoot to rise above its branches."
Ch'ang had nothing to say. Hsiu returned and told the story of his conversation to San-sheng. San-sheng unconsciously stuck out his tongue [in surprise] and said: "He has surpassed Lin-chi by seven paces."
If you are able to understand and make clear these words, then I will acknowledge that you have a certain degree of responsiveness to the teachings. Why is this so? If you speak to yourself while no one is around, you behave as meanly as a rat. What can anyone possibly prove [about your understanding]?
I also think it's a good way to measure Spiritual Hucksterosity.
HT to Gniz, whose post about Andrew Cohen (I just can't get over that people take that guy seriously) reminded me of this bit by Hakuin.