"... count it all joy when you fall into various trials, knowing that the testing of your faith produces patience. But let patience have its perfect work, that you may be perfect and complete, lacking nothing." James 1.2-4Joy during good times is normal.
Joy during times of trial seems contradictory. Doesn't it?
Tests of faith only happen in the lives of those who live by faith.
They live by faith because they are of God. This does not give them a reason to be improperly joyful, but to be filled with a great joy.
This is the joy of being a child of God.