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

by the party challenging his or her competency. (People v. Blacksher (2011) 52 Cal.4th 769, 797; People v. Kaplan (2007) 149 Cal.App.4th 372, 382-383.)

Evidence of incompetence may emanate from several sources, including the defendant's demeanor, irrational behavior, and prior mental evaluations. A reviewing court gives great deference to the trial court's decision whether to hold a competency hearing. When there is less than substantial evidence, the trial court still has discretion to order a competency hearing. The trial court's decision whether to order a competency hearing is given great deference because the trial court has had the opportunity to observe the defendant during trial. (People v. Kaplan, supra, 149 Cal.App.4th at p. 383.)