What is the test for qualified immunity in the context of civil litigation?

The doctrine of qualified immunity shields government officials from suit concerning acts undertaken in the course of their duties if "their conduct does not violate clearly established statutory or constitutional rights of which a reasonable person would have known." Harlow v. Fitzgerald, 457 U.S. 800, 818, 102 S.Ct. 2727, 2738, 73 L.Ed.2d 396 (1982). This protection not only insulates the officials from liability, but it also conveys a concomitant "entitlement not to stand trial or face the other burdens of litigation," Mitchell v. Forsyth, 472 U.S. 511, 526, 105 S.Ct. 2806, 2815, 86 L.Ed.2d 411 (1985), including the conduct of pretrial discovery, id.