Is a plea condition that a witness must agree to testify in the context of immunity valid?

Second, even assuming defendant had presented the argument below, he fails to show that the plea condition was impermissibly coercive. As we observed in People v. Allen (1986) 42 Cal.3d 1222, 1251-1252, 232 Cal.Rptr. 849, 729 P.2d 115: " '[A] defendant is denied a fair trial if the prosecution's case depends substantially on accomplice testimony and the accomplice witness is placed, either by the prosecution or by the court, under a strong compulsion to testify in a particular fashion.' ... Thus, when the accomplice is granted immunity subject to the condition that his testimony substantially conform to an earlier statement given to police ... or 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 [53 Cal.3d 1217] that an agreement requiring only that the witness testify fully and truthfully is valid." (Italics added.)