It does not provide the reason for testing. There is no reason for God to test anyone if He knows our hearts and minds.
But that presumes that God tests principally for His own benefit. That cannot be so for the very good reason you give. We are tested for OUR benefit. Have you ever been through a trial and come out better spiritually? Of course, we all have.
Maybe some desire to be tested; others are happy the way they are. You keep telling me how secure you are in your belief. Do you need to go through a Job-like trial to feel "better" about it?
And, besides, since when does God do things on our agenda if everything is subject to fulfillment of His "plan?"