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

"[A] trial court is obligated to conduct a full competency hearing if substantial evidence raises a reasonable doubt that a criminal defendant may be incompetent. This is true even if the evidence creating that doubt is presented by the defense or if the sum of the evidence is in conflict. The failure to conduct a hearing despite the presence of such substantial evidence is reversible error." (People v. Lightsey (2012) 54 Cal.4th 668, 691.)