Assume God is omniscient and man has free will. God therefore knows what a person will do before he does it, and a person is free to choose what he wants to do.
But if a person decides to do something different than what God knows he will do, then by simple logic the part of the initial assumption about God's omniscience is incorrect.
Or if a person always ends up doing precisely what God knows he will do, then by simple logic the part of the initial assumption about free will is incorrect.
There cannot be Godly omniscience and free will by God's subjects in the same universe.
First of all, how would we test it? How would we know what God
knew and did not know before the fact? Second, if free will is defined as "doing something other than what God knows" I would argue that yes, we don't have true free will nor should we. You don't get to out think God. Ain't gonna happen. Whether or not you judge Him evil for foreknowing your damnation, for example, matters not since even if He
did foresee it, you chose it. The protest that you simply couldn't have done anything nor chosen any way to avoid it is whining after the fact at best.