What is the legal test for mental competence of a defendant in a criminal case?

It is well established that the criminal trial of an incompetent defendant violates the defendant's right to due process. (Medina v. California (1992) 505 U.S. 437, 453; People v. Weaver (2001) 26 Cal.4th 876, 903.) When a criminal defendant's attorney informs the court of his or her belief that the defendant may be mentally incompetent, the court is required to order that the question of the defendant's mental competence be determined in a hearing held pursuant to sections 1368.1 and 1369. ( 1368, subd. (b).) Criminal proceedings are suspended pending the competence determination. (Id., subd. (c).)