What is the test for determining whether a defendant has a mental disorder or developmental disability?

disorder or developmental disability, the defendant is unable to understand the nature of the criminal proceedings or to assist counsel in the conduct of a defense in a rational manner." ( 1367, subd. (a); People v. Halvorsen, supra, at p. 401.)

"Evidence of incompetence may emanate from several sources, including the defendant's demeanor, irrational behavior, and prior mental evaluations. [Citations.] But to be entitled to a competency hearing, 'a defendant must exhibit more than . . . a preexisting psychiatric condition that has little bearing on the question . . . whether the defendant can assist his defense counsel.'" (People v. Rogers (2006) 39 Cal.4th 826, 847; People v. Sattiewhite (2014) 59 Cal.4th 446, 464-465.)