Regarding the testing of our faith, first of all, we know that God tests the faith of those who follow Him. Consider James 1:2-4: “Count it all joy, my brothers, when you meet trials of various kinds, for you know that the testing of your faith produces steadfastness. And let steadfastness have its full effect, that you may be perfect and complete, lacking in nothing.” God lets hard things happen that He then uses to test or “refine” us—think like a testing of metal by fire to gain a pure product. And He works​ all things together for our good (Romans 8:28) to shape us into the image of Christ (Romans 8:29). The greatest love is shown by seeking our highest good, and we are a long way from being like Christ, so the refining goes on. 

Concerning whether Satan can test us like God allowed to happen with Job, there appears to be evidence of his ability to test us in the New Testament (even though Satan was in many ways defeated at the cross). Jesus is our example for us to follow in His steps, and He was tested by Satan in the wilderness as soon as He started His ministry and was filled with the Holy Spirit (Matthew 4). Then Paul speaks of some sort of “messenger of Satan” sent to torment him (2 Corinthians 12:7), and though he doesn’t describe what this is, it appears to give credence to the idea that God allows the enemy to test as in ways as Jesus was tested. However, once a person trusts in Christ, for them, Satan is essentially disarmed at the cross and no longer has power over them (Colossians 2:13-15). That’s essential for us to remember! 

God is forever committed to working all of this out for our good and drawing us closer to Himself. His ultimate goal is to make us like His Son so that His joy may be in us and our joy may be complete (John 15:11). No matter what trials and testing we experience, we can be confident that “He who has begun a good work in you will complete it until the day of Jesus Christ” (Phillipians 1:6).