Christians call it a testimony. The Bible teaches us that each individual must have their own. It is their own relationship with God and their eternal future.
Acts 4:12 "Salvation is found in no one else for there is no other name under Heaven give to men by which we must be saved."

I was raised in church from the time I was born. Both parents are Christians. When I was about 8 I felt like I was under conviction to ask Jesus in my heart. I wanted what the preacher talked about, my parents had, and what I learned to sing about in Sunday School. It wasn't enough that I was a good person or parents good or haven't committed in big sins. My parents couldn't do it for me. Every person has to make this decision on their own. To say I am sorry for my sins, and turn from them and ask Christ to have all of my heart.
Isaiah 64:6 "All our righteous acts are like filthy rags."
I talked to my pastor and ask Jesus in my heart and was baptized. This is at the point where most people say they had peace the rest of their lives in this area. But I can't say that. I never drifted far away or had a wild life but never peace about my salvation. Wasn't sure of it. So when I was in my early twenties we had a service at church where several leaders admitted they were uncertain. They were telling my story. So I went down during invitation and talked with the pastor. He had told a story of a man kneeling and putting a stake in the ground and saying this stake would serve to remind him of the place where he nailed down his salvation. He can go back to this moment if he doubted again.
I had a peace that night that has never gone away. I have had seasons of my life where I didn't follow Christ as close as I should but I never had any doubts of salvation. I have total peace that I am. I won't know this side of Heaven if I was saved at 8 or in my 20's.
John 3:16 "For God so loved the world that He gave His only begotton Son that whosoever believed in Him will not perish but have everlasting life."