Number 5, from section 2 (WORDS), in Rules of a Godly Life:
Confide to no one your personal secrets unless you have beforehand found him to be worthy of your trust. Here is one way to prove him and learn to know him well: confide to him some secret of small importance; if he keeps it to himself it is an indication of his trustworthiness. However, it is not wise to inform any friend carelessly of all your secrets. There is a possibility that at some later time you may have sharp differences and then he may use his knowledge to your harm.