Why did Elijah send the servant back seven times?

Answer:

"Now Elijah said to Ahab, "Go up, eat and drink; for there is the sound of the roar of a heavy shower." So Ahab went up to eat and drink. But Elijah went up to the top of Carmel; and he crouched down on the earth and put his face between his knees. He said to his servant, "Go up now, look toward the sea." So he went up and looked and said, "There is nothing." And he said, "Go back" seven times.  It came about at the seventh time, that he said, "Behold, a cloud as small as a man's hand is coming up from the sea." And he said, "Go up, say to Ahab, 'Prepare your chariot and go down, so that the heavy shower does not stop you.'" In a little while the sky grew black with clouds and wind, and there was a heavy shower. And Ahab rode and went to Jezreel" (I Kings 18:41-45).

We assume that while Elijah was crouched down with his face between his knees that he was praying, but that isn't directly stated in this text. Rather, we learn about the prayer in "Elijah was a man with a nature like ours, and he prayed earnestly that it would not rain, and it did not rain on the earth for three years and six months. Then he prayed again, and the sky poured rain and the earth produced its fruit" (James 5:17-18).

I doubt this was a test of the servant, but rather a test of Elijah's persistence. It teaches us that God answers prayers when He sees it is best and not when men think the answer ought to be given. "Then He spoke a parable to them, that men always ought to pray and not lose heart" (Luke 18:1).