Why does God test us?
No one likes testing, trials and tribulations, but they are necessary in order for every believer to grow into a mature disciple. God does not test or try us to see how holy or mature we are. He already knows that. He tests us and allows us to go through trials and tribulations to show us, and those around us how mature and holy we are.
When we fail the trial we realize that we "are but beasts" (Ecclesiastes 3.18). He also does this to induce maturity. Spiritual growth comes only through trials, tribulations and testing. Without them a Christian remains a spiritual infant incapable of serving God.
"And not only that, but we also glory in tribulations, knowing that tribulation produces perseverance; and perseverance, character; and character, hope. Now hope does not disappoint, because the love of God has been poured out in our hearts by the Holy Spirit who was given to us" (Romans 5.3-5).
"My brethren, 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 1.2-4).
The more tribulations, trials and testing you go through the more you will either grow spiritually or backslide. Hopefully most serious believers will grow and mature in the Lord. If you seek to live a holy life for God you will be persecuted (2 Timothy 3.12). Some believe Paul was the greatest Christian man to ever live. Why? He suffered more than anyone else and he grew through his sufferings (Acts 9.16; 20.23; 1 Thessalonians 3.3; 2 Corinthians 6.4-5; 11.23-27; 2 Timothy 1.8, 12; 2 Timothy 2.3, 9).