From Heaven's Desk---The Test, the Tester and the Testee.

Psalm 139:23-24.
Examine me, O God, and know my mind;
      test me, and discover my thoughts.
 24 Find out if there is any evil in me
      and guide me in the everlasting way.

Affirmation of the Fact that God alone is all Knowing: Even we Humans do not know ourselves as much as the creator does know us. Same way a computer tablet does not know its capabilities more than The "Steve Jobs" or "Bill Gates" that made  it. To discover who we truly are and what we are capable of doing is best done when we pass through the Test. A personal experience does affirm this fact: a believe I hold so dearly. Little wonder the Bible says that every Man's work will be tested by the fire 1 Cor 3:13----his work will be shown for what it is, because the Day will bring it to light. It will be revealed with fire, and the fire will test the quality of each man's work.
Even the man after God's own heart could affirm the all-knowing capability of God. The Psalmist knew that his real and true character would not be brought out when all going was good, but it will be brought out at those stages in Life where we have to step to the next level. The stage of the Test.
I always love to relate every spiritual lesson to what we can see here physically(because after all, the physical is a shadow of every thing done in the spiritual). Just as a student's real capability is brought out during the examinations, so does Life brings out our different forms during its "Test stages".
Prov 24:10---If thou faint in the day of adversity, thy strength is small.
The psalmist asked God to Test Him and discover his thought; what a request to make. But as known, true spiritual maturity lies in boldness-----2 Tim 1:7 For God did not give us a spirit of timidity, but a spirit of power, of love and of self-discipline.

Even Elijah put God almighty to the test. As great a prophet he was, he knew that the true capability of the all-conquering God could only be affirmed if he was put to a sterner test. After all if something is humanly possible, then there is no need for a miracle in the first place. Evening approaches and Elijah takes twelve stones, according to the number of the Tribes of the sons of Jacob, and builds an altar IN THE NAME OF THE LORD.  He put the wood in order and cut the bullock in pieces and placed it atop the wood.  Then, Elijah filled four barrels with water and poured them on the bullock and the wood, not once, not twice, but three times!  At the time of the evening sacrifice, the Prophet Elijah came near and called on the Lord GOD of Abraham, Isaac, and of Israel to let it be known that “Thou art God in Israel, and that I am thy servant, and that I have done all these things at thy word.”  Elijah continued on to make sure that Israel and the prophets of Baal made no mistakes about this most important event that would prove the existence of the ONE True GOD, the GOD of Israel and all that HE requires of HIS People and of the Stranger who wishes to worship HIM.