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

^2. This is in contrast to the substantial evidence standard, which is applied by the trial court in determining whether to hold a competency hearing. (See People v. Mai, supra, 57 Cal.4th at p. 1032 ["[T]he trial court must suspend criminal proceedings and conduct a competency hearing if presented with substantial evidence that the defendant is incompetent."].)