John 7:17 If any man will do his will, he shall know of the doctrine, whether it be of God, or whether I speak of myself.
Testimony comes by faith which is to say that it is in the doing that spiritual confirmation occurs. As we act on spiritual promptings or prove the lord by keeping his commandments we become better able to hear and respond. It is like any practice, as I practice I become better, tasks become easier. If I want a testimony I must practice the underlying principles and then I will gain the testimony.