Most of what are called testimonies are not testimonies. They are boasting. A Christian testimony is not what God has done for you.
The apostle Paul experienced many things that God brought Him through, and also heavenly visions and such, yet he called these "boasting" (2 Cor 11:21, 11:30). And then he says he refrains from this kind of boasting:
2 Cor 12:6 "Even if I should choose to boast, I would not be a fool, because I would be speaking the truth. But I refrain, so no one will think more of me than is warranted by what I do or say,"
When the focus of a testimony is "what God has done for me", the attention on the "me", or the self.
Paul says:
2 Cor 12:11 "You have made me act like a fool--boasting like this. "
Testimonies where we boast about what God has done for us, makes us look foolish.
So what is the proper Christain testimony? Our testimony is us being a witness to the resurrected Christ. This is what we have seen, heard, and known and experienced of Christ, and also what manner of Christ we display in our daily lives.
A man who boasts about all the miracles, healings and things God has done for him, yet he lets his temper loose on his wife, or children, is not bearing the testimony of Christ.
Acts 23:11 11 The following night the Lord stood near Paul and said, “Take courage! As you have testified about me in Jerusalem, so you must also testify in Rome.”
Acts 2:32 "God has raised this Jesus to life, and we are all witnesses of it."
Most Christians may not have a healing or miracle story, but every Christian can testify that Christ is risen. Our testimony is our witness of the resurrected Christ. Today the resurrected Christ lives in us by His Spirit, and so we all can testify something of our experience of Christ to edify others and convert unbelievers.
If I can give an example, imagine that we have cups, and God is the water. Imagine someone holding the cup with water in it, and telling us how great the cup has become since the water is in it. This is like a person saying how great they have become since God did all these wonderful things for them. But I have a cup also, and it is empty. I don't care about how good your cup looks since the water is in it, I am thirsty and I need a drink, so when will you pour out the water in your cup, so I can drink and satisfy my thirst? A testimony should satisfy people's thirst for the living God, and this is done by us being witnesses that Christ is resurrected and He is the living water available to satisfy the thirst of anyone who believes into Him. Our testimony is the living waters, that flows from within us to satisfy the thirsting of others:
John 7:38 He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water.
