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

Also, because there was not substantial evidence that defendant was incompetent, the trial court did not abuse its discretion in failing to appoint an expert. (People v. Ramirez (2006) 39 Cal.4th 398, 431 [finding no abuse of discretion when "there was no substantial evidence that defendant was mentally incompetent. Defense counsel's request for a 'psychiatric evaluation' of defendant, standing alone, does not require the court to appoint such an expert or conduct a competency hearing"].)

c. The trial court did not abuse its discretion when it denied plaintiffs motion for a new trial.