There is a popular expression that someone has “the patience of Job,” probably based on a reference in the New Testament letter of James: “You heard about the patience of Job” (James 5:11). Job’s patience had apparently become proverbial by the time the letter of James was written, probably around the middle of the first century CE. But when we read the biblical book of Job we are hard-pressed to find much evidence of Job’s patience. The Greek word (ὑπομονή hypomonē) translated “patience” in James could equally mean “endurance” or “steadfastness”, but these are hardly major themes in Job either. Job is hardly a paragon of patience or endurance. In fact, he even protests that he has every right to be impatient! “Why should I not lose my patience?” (Job 21:4 NJPS). He constantly protests his innocence, complains that he is suffering without cause, and demands justice. The only time the word ὑπομονή hypomonē appears in the Greek version of Job is to say that God is wearing out Job’s patience, like water wears down rocks (Job 14:19LXX)! So where did James get the idea that Job was a model of patience or endurance?
David deSilva  argues convincingly that, rather than quoting from the biblical book of Job, James was more likely referring to the Testament of Job (hereafter TJob), a pseudepigraphical work probably written in the first century BCE or first century CE. TJob is based on the canonical Job but the emphasis is different: this Job is a model of endurance, and the word ὑπομονή hypomonē used by James occurs several times throughout the book. DaSilva points to linguistic similarities between James 5:7–11 and TJob and argues that James learned a version of the story of Job from a tradition beyond the canonical Job that came to written expression in TJob, which “presents a fully developed picture of Job as an athlete of endurance, holding on to his commitment to obey the One God and empowered to bear any temporal loss by God’s promise of a future reward for the righteous”. James’s brief reference to the patience/endurance of Job would presume that his audience knows the reshaped Job story from a version such as TJob and that it is this tradition, rather than the biblical book of Job, to which he refers.
 “The Testament of Job: Job Becomes an Example of Patient Endurance”, chapter 9 in The Jewish Teachers of Jesus, James, and Jude: What Earliest Christianity Learned from the Apocrypha and Pseudepigrapha, Oxford University Press, 2012, pp. 237-251.