Well, no one can have a testimony without first having victory over a test, and one cannot be a witness unless they have witnessed something. Jesus did both of these things. He came to earth as a man, being tempting in every way, being persecuted in every way yet there was no sin found in Him. He did nothing that He didn't first see His Father in heaven do. He is the faithful witness that we look to for our encouragement, knowing that He now sits at the Fathers right hand.
Even though most of us have not been persecuted physically or even mentally as Jesus was, we still have a measure of this we walk through everyday in facing the world, however, I believe that in the days to come persecution for the believer will intensify and without holding on tightly to the "faithful witness" Jesus Christ, we will not be able to with stand it.
The testimony and witness that we have is also very important to others. Just knowing that someone else has walked through a test and now is a witness to the grace and mercy of God is a encouragement to others.