Did Abraham know that sacrificing Isaac was a test?

God promised Abraham many descendants (Ge 13:16) through Isaac (21:12).

But then in Ge 22:

1 After these things God tested Abraham and said to him, “Abraham!” And he said, “Here I am.” 2 He said, “Take your son, your only son Isaac, whom you love, and go to the land of Moriah, and offer him there as a burnt offering on one of the mountains of which I shall tell you.”

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The narrator mentioned that it was a test. However, it was not explicitly told to Abraham that it was. Abraham took God's command seriously whether or not it was a test.

3 So Abraham rose early in the morning, saddled his donkey, and took two of his young men with him, and his son Isaac. And he cut the wood for the burnt offering and arose and went to the place of which God had told him. 4 On the third day Abraham lifted up his eyes and saw the place from afar. 5 Then Abraham said to his young men, “Stay here with the donkey; I and the boy will go over there and worship and come again to you.”

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Abraham seemed to have some inking that things would work out somehow. He 11:

19a He considered that God was able even to raise him from the dead.

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Abraham trusted God so much that he was willing to go all the way to kill Isaac.

Did Abraham know that God's commanding him to sacrifice Isaac was a test?

He might have an inkling of it. In any case, he obeyed God's command on face value. He didn't even question God about it. His faith was strong.