Jamieson, Fausset and Brown on Genesis 44:5

5. Is not this it in which my lord drinketh--not only kept for the governor's personal use, but whereby he divines. Divination by cups, to ascertain the course of futurity, was one of the prevalent superstitions of ancient Egypt, as it is of Eastern countries still. It is not likely that Joseph, a pious believer in the true God, would have addicted himself to this superstitious practice. But he might have availed himself of that popular notion to carry out the successful execution of his stratagem for the last decisive trial of his brethren.