What is the test for determining whether a defendant is competent to stand trial?

In summary, defense counsel must present expert opinion from a qualified and informed mental health expert, stating under oath and with particularity that the defendant is incompetent, or counsel must make some other substantial showing of incompetence that supplements and supports counsel's own opinion. Only then does the trial court have a nondiscretionary obligation to suspend proceedings and hold a competency trial. (See People v. Pennington, supra, 66 Cal.2d at p. 518, 58 Cal.Rptr. 374, 426 P.2d 942.) Otherwise, we give great deference to the trial court's decision not to hold a competency trial.