Deceitful spirits? (1 Kings 22; 2 Chronicles 18)

It is somewhat disconcerting that a group of prophets all gave Ahab poor advice.  When Micaiah is brought before the kings and given the opportunity to prophesy he comments that God, in His ultimate sovereignty, sent a deceitful spirit to send Ahab down the wrong path.  To me, this is one of those "what in the world?" passages that doesn't seem to make much sense.  Why would God send a spirit to deceive Ahab?  Unfortunately, I don't know that there are any clear answers to that question other than the idea that maybe God was testing Ahab to see what he would do.  Would he listen to the advice he wanted to hear, or would he heed the warnings from a prophet whom he despised?  The reality is that Ahab usually did what Ahab wanted to do irregardless of what the Lord wanted, and it is conceivable that this was just one more instance of him going his own way.  God did give Ahab an opportunity to choose wisely, but his hatred of Micaiah seems to have encouraged him to choose otherwise.  This fatal mistake cost him his life.