Jamieson, Fausset and Brown on Genesis 42:9-14

9-14. Ye are spies--This is a suspicion entertained regarding strangers in all Eastern countries down to the present day. Joseph, however, who was well aware that his brethren were not spies, has been charged with cruel dissimulation, with a deliberate violation of what he knew to be the truth, in imputing to them such a character. But it must be remembered that he was sustaining the part of a ruler; and, in fact, acting on the very principle sanctioned by many of the sacred writers, and our Lord Himself, who spoke parables (fictitious stories) to promote a good end.