In Linhart v. Nelson (1976) 18 Cal.3d 641, the California Supreme Court was called upon to interpret Code of Civil Procedure sections 657 and 658. Section 658 provides that when an application for a new trial is made upon the ground of newly discovered evidence (and several other grounds), it "must be made upon affidavit." The Linhart court held that, in view of the mandatory nature of the language of section 658, a motion for a new trial on any such ground had to be presented solely by affidavit and determined solely on the affidavits presented; that the testimony of witnesses was impermissible on any hearing to determine the motion for a new trial.