Is a plea agreement requiring only that a witness testify fully and truthfully valid valid?

that his testimony result in defendant's conviction . . . the accomplice's testimony is "tainted beyond redemption" and its admission denies defendant a fair trial. On the other hand, although there is a certain degree of compulsion inherent in any plea agreement or grant of immunity, it is clear that an agreement requiring only that the witness testify fully and truthfully is valid.'" (People v. Sully (1991) 53 Cal.3d 1195, 1216-1217, italics omitted.) We review the trial court's evidentiary ruling for an abuse of discretion. (People v. Brown (2003) 31 Cal.4th 518, 536.)