What is the test for competence to stand trial in a mental health case?

"A defendant who, as a result of mental disorder or developmental disability, is 'unable to understand the nature of the criminal proceedings or to assist counsel in the conduct of a defense in a rational manner,' is incompetent to stand trial. ( 1367.) When the accused presents substantial evidence of incompetence, due process requires that the trial court conduct a full competency hearing. [Citation.] Evidence is 'substantial' if it raises a reasonable doubt about the defendant's competence to stand trial. [Citation.]" (People v. Jones (1991) 53 Cal.3d 1115, 1152.)

"Once a defendant has been found competent to stand trial, a second competency hearing is required only if the evidence discloses a substantial change of circumstances or new evidence is presented casting serious doubt on the validity of the prior finding of the defendant's competence. [Citations.]" (People v. Medina (1995) 11 Cal.4th 694, 734.)