Revelation 12:11 (KJV)
And they overcame him by the blood of the Lamb, and by the word of their testimony; and they loved not their lives unto the death.

Testifying to the goodness of God is an effective way to encourage fellow believers and highlight the grace, power, and love of God to the outside world.
Most commonly, we testify to share how we became Christians by God’s miraculous intervention and His work in our lives through specific events. Through our walk with the Lord, we experience supernatural events that we share with others to reinforce their faith that keeps us in God.
Sharing our testimonies or testifying to the goodness of God in our lives is a way of showing our gratitude to God, by not keeping what He’s done for us to ourselves.
It is a way of showing others the power and grace of God and our dependency on Him and the one sure way to putting the enemy to shame and defeating his plans and purposes towards us.
If the legal system requires more than one witness to establish a matter according to Deuteronomy 19:15, the court of heaven with the magnitude of heavens mandate requires every Christian to witness the matter of the cross, the body, the blood, and the finished work.
We overcome the enemy on account of and by Christ having shed His blood. Had it not been shed, Satan’s accusations would have been unanswerable; as it is, that blood meets every charge.
As powerful as the blood of Jesus is, it still requires the account of our testimonies. Our testimonies evidenced our victory over Satan.
Our testimonies should not begin and end with the conversion experience but should also include how the Lord has worked in our lives to sanctify us for His service.
A testimony could include how He brought us through a challenging time in life (such as overcoming loss or some severe illness) and built our faith in Him through that experience. We should also be able to describe the continual process by which the Spirit who now indwells us leads, guides, and shapes us into mature Christians. Again, the focus should be on the Lord and His faithfulness and should include at least one verse that speaks of that faithfulness like Psalm 18:2, 6.
What we do with our testimonies is lay a case for the bible and display the evidence collected based on the question that many have been asked by us or others to know if the Bible is reliable?
We can confirm the accuracy of the bible in all areas of our lives, which I think we do through our testimonies, we can gain confidence that the Bible is truly the Word of God, and we witness to that according to Luke 24:48.
Testify means to boast or to glory in the Lord according to Psalm 34:2. Boasting in the joy, strength and grace bestowed upon us and glorying in His presence says Isaiah 41:16.
When God does something life-changing in our lives, He does so not only for our benefit but for His glory. We owe it to Him and to others to testify to His goodness.
Let Psalm 89 be your anthem, sing aloud of God’s goodness and His wondrous works in your life. Testify what the Lord has done and put the enemy to shame.
Shalom