What is the legal test for failing to disclose evidence relevant to the impeachment of a prosecution witness?

Failure to disclose evidence relevant to the impeachment of a prosecution witness requires reversal "only if the evidence is [802 P.2d 397] material in the sense that its suppression undermines confidence in the outcome of the trial." (United States v. Bagley (1985) 473 U.S. 667, 678, 105 S.Ct. 3375, 3381, 87 L.Ed.2d 481.) Otherwise stated, reversal is required "only if there is a reasonable probability that, had the evidence been disclosed to the defense, the result of the proceeding would have been different." (Id. at p. 682, 105 S.Ct. at p. 3383.)