Abraham knew it was a test.

Gen 22:7 says, “Behold the fire and the wood: but where is the lamb for a burnt offering?

22:8 And Abraham said, My son, God will provide himself a lamb for a burnt offering: so they went both of them together.”  OK, they gave the plot away here.  If Isaac was going to be the sacrifice then why would Abraham say god would provide the sacrifice?  It is going to be Jesus.