"And you shall remember all the way which the Lord your God has led you in the wilderness these forty years, that He might humble you, testing you, to know what was in your heart, whether you would keep His commandments or not," (Deut. 8:2).
Basically, the open theist position on this verse is that since God does not know the future, He had to test people to see what was in their hearts. But there is a problem here, because in open theism God knows all present things exhaustively. If God was going to test people to see what was in their hearts, does that mean God did not know what was already there? That would make no sense, even in open theism. If the open theist says that God's test was to discover what would be in their hearts later, then I point them back to the text which does not speak that way. It speaks of the past.
Deut. 8:2 is an example of anthropomorphism combined with a testing expression; that is, God is speaking in human terms and human ways for the benefit of the people. In this case, it is to reveal to them the quality of their faith before God.
God knows all things (1 John 3:20). He tests people not to determine that which He does not know, but because God is working within our time frame. God condescends to teach us and to reveal His will to us.