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

When defense counsel has presented substantial evidence that a defendant is incompetent to stand trial, the trial court must declare a doubt as to the defendant's competence and suspend proceedings even if the court's own observations lead it to believe the defendant is competent. (People v. Pennington (1967) 66 Cal.2d 508, 518, 58 Cal.Rptr. 374, 426 P.2d 942.) But when, as in this case, a competency hearing has already been held, the trial court may appropriately take its personal observations into account in determining whether there has been some significant change in the defendant's mental state. This is particularly true when, as here, the defendant has actively participated in the trial. The trial court had an opportunity to observe, and converse with, defendant throughout the trial itself and the posttrial proceedings. The court appropriately considered these observations in concluding that defendant's condition was essentially unchanged from the start of trial, when the court found him competent, to the time he was sentenced, when defense counsel asked that proceedings again be suspended.