Genesis 44:4
And when they were gone out of the city, and not yet far off, Joseph said unto his steward, Up, follow after the men; and when thou dost overtake them, say unto them, Wherefore have ye rewarded evil for good? And when they were gone out of the city, and not yet far off, Joseph said unto his steward, Up, follow after the men; and when thou dost overtake them, say unto them, Wherefore have ye rewarded evil for good?
The verse records Joseph's command to his steward to pursue the men, overtake them, and confront them with having repaid good with evil. The order was to be carried out just after they had left the city, while they were still close at hand and not yet far off. The charge turned on a silver cup that Joseph himself had caused to be hidden in Benjamin's sack. In that charge the brothers stood accused of taking the ruler's silver cup from his house.
Rulers' drinking cups were believed to detect poison and were prized as a sure safeguard against murder by poisoning, and that belief gives the steward's question about the cup its force. The steward's charge further presented Joseph as using the cup for divining. Joseph did not himself claim the power of divination, but he allowed his brothers to think he could read their secrets.
Joseph devised and arranged the accusation and the search as a test of his brothers. The test was meant to draw from them an acknowledgment of their sin. It was also meant to show whether they would abandon Benjamin as they had once abandoned Joseph, thereby revealing their feelings toward him.