Why Would an Omniscient God Test Hezekiah to Know What Was in His Heart?

Questions about how the death of David’s son squares with Ezekiel 18:20, what 2 Chronicles 32:31 means when it says God tested Hezekiah’s to know what was in his heart, and financing the wedding of a child who may marry an atheist.

• How does 2 Samuel 12:13–14, where King David is told his child will die because of his sin, square with Ezekiel 18:20, which says the one who sins will die and the child will not share in the guilt of the parent?
• What does it mean in 2 Chronicles 32:31 when it says God left Hezekiah in order to “test him and know what was in his heart,” when God is omniscient?
• Should we finance the wedding of our daughter who is not practicing her faith and may marry an atheist?