The book of Job describes a conversation between the devil and Jehovah, as everyone knows. However, Satan knew Jehovah intimately and would have been well aware of Jehovah's ability of foreknowledge. One would have to imagine that Jehovah could have easily just told Satan that Job would in fact be faithful and therefore spared Job the agony he went through, as he had insight because of his foreknowledge that the spirit creatures should have understood.
Did Jehovah and Satan have a high-stakes game going? Was Job and his family the ante? That's what is seems like, but then the foreknowledge question needs to be dealt with.
You're assuming as most Xians do that the character mentioned and even translated as Satan IS the same character.
HOWEVER, remember that early Hebraic thought didn't include the notion of a Satan/Devil; so realize that whenever you see Satan mentioned in the OT, it was likely a later addition to the translations (e.g. Septuagint) to support the Xian concept. The practice starts early in Genesis, eg Gen 3:15, where the serpent is interpreted by Xians as Satan in disguise, and the scripture is seen as the first foreshadowing (prophecy) of Jesus.
But back to Job: Realize that Job's account was likely one of the oldest books of the OT, likely written before the Torah.
From http://bible.cc/job/1-6.htm
Barnes' Notes on the Bible
It (Satan) was a word, therefore, early used in the sense of an adversary or accuser, and was applied to anyone who sustained this character, until it finally came to be used as a proper name, to denote, by way of eminence, the prince of evil spirits, as the adversary or accuser of people.
An opinion has been adopted in modern times by Herder, Eichhorn, Dathe, Ilgen, and some others, that the being here referred to by the name of Satan is not the malignant spirit, the enemy of God, the Devil, but is one of the sons of God, "a faithful, but too suspicious servant of yahweh." According to this, God is represented as holding a council to determine the state of his dominions. In this council, Satan, a zealous servant of yahweh, to whom had been assigned the honorable office of visiting different parts of the earth, for the purpose of observing the conduct of the subjects of yahweh, makes his appearance on his return with others.
Similarly, the claims of God possessing omniscience was NOT common in the OT, but grew increasingly common as time went by (eg in Isaiah, likely written hundreds of years after Job's account). Readers of OT cannot assume God's divine fore-knowledge as existing throughout, since it wasn't ascribed to God in Genesis (e.g. implications of the original sin, or YHWH's infamous 'double regret' in Noah's flood, etc, etc).
Here's a funny YouTube video on Job:
http://www.youtube.com/watch?v=QVgZqnsytJI
