A testimony comes from believing. It is not the product of knowledge.
I often consider mine will be thought of as a weak testimony if I say I believe instead of saying I know the church is true. But, perhaps, as I said, testimony comes from believing, not from knowledge.
I think on John 16:7, and wonder if I understand it better than I ever have. "It is expedient for you that I go away: for if I go not away, the Comforter will not come unto you; but if I depart, I will send him unto you."
As long as Christ was there, their testimonies were testimonies of sureness, of knowledge. But, without him, they had to live by faith, their belief had to be enough. I do not know, and know I can be wrong in how I understand the scriptures, but I wonder if what I have just said is so.
If a person knows something, he has no cause to belief, no cause for faith, for he knows it. I don't have time to look it up, but there is a scripture to that effect.