Genesis 44:2

Put my cup. This was Joseph’s final and decisive test prior to revealing himself to his brothers. His purpose was to create a situation by which he could legitimately claim the right to retain Benjamin in Egypt, so that his brothers might have an excuse for returning to Canaan without the favorite of their father. By this he would learn beyond a doubt what kind of men they now were. Either they would abide by the decision of Joseph to keep Benjamin in Egypt and return to their father with the heartbreaking message that he must reconcile himself to the loss of the remaining son of his beloved Rachel, or they would do everything in their power to prevent such a misfortune.