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The bible does not speak of "testing our mettle". God wants us to have a good life, but there is always somebody who thinks he has a better idea. For instance, that is a Jewish prayer, not Christian.
By "good" I expect you mean "virtuous" - albeit to the extent that we can given our human limitations and frailties. And isn't the conscious choice of leading a virtuous life a test of our mettle, or calibre, or whatever you might want to call it?
Ok, if that's what you want to believe. But you didn't get it from the bible, so don't blame it on God.
3Give us day by day our daily bread.
4And forgive us our sins; for we also forgive every one that is indebted to us. And lead us not into temptation; but deliver us from evil."
Did you say the Lord's prayer is not a Christian prayer?