If you don't know you have a new-hearted identity in Christ, the following passage from the Old Testament will be understandably troubling for you:
Remember how the Lord your God led you all the way in the desert these forty years, to humble you and to test you in order to know what was in your heart, whether or not you would keep his commands. [Deut. 8:2]
If I had read that passage ten years ago, I would have drawn some horrible conclusions about my heart - wrongly assuming that:
"There is possibly something in my heart that I shouldn't trust - something that could prevent me from following his commands."
God's audience at that time was not new-hearted, Spirit-indwelled:
Why did God need to "test" something he already knew? His omniscience would have told him what was already in their hearts. They were not yet new hearted, Spirit-changed people. Jesus had not come to bring them that yet. That would be later in history.
Perhaps it was the people themselves that needed to know what was in their hearts, and experience the futility of living under a broken [ill-functioning] heart? People often need to feel the crushing burden of living as a self-indulgent corpse before they are ready to live as a free-hearted and alive son or daughter.
What we need to know today:
Secondly, the primary point of Jesus' rescue of us is to give us a heart that loves God and leaves no room for doubt as to its allegiance. And, being an in-Christ person, that faithful heart is already in you. When you enter friendship with Jesus, he surgically removes the wandering heart and replaces it with a heart that is aligned and allied with God.
You can trust the faithfulness of your new heart.