What is the legal test for mental competence to stand trial?

3 The question of mental competence to stand trial ( 1368) is whether at time of trial the accused is able to understand the nature and purpose of the proceeding against him and to assist his attorney to conduct his defense in a rational manner. The legal defense of insanity ( 1026) poses separate and distinct questions of whether an accused at time the offense was committed understood the nature and quality of his act and was able to distinguish right from wrong. (People v. Corona, supra, 80 Cal.App.3d 684, 713, 145 Cal.Rptr. 894.)