What is the test for establishing a defendant's competency to stand trial?

institute competency proceedings therefore violated a petitioner's right to procedural due process, the reviewing habeas court considers "whether a reasonable judge, situated as was the trial court judge whose failure to conduct an evidentiary hearing is being reviewed, should have experienced doubt with respect to competency to stand trial." Stanley v. Cullen, 633 F.3d at 860 (citation omitted).

A defendant is considered competent for constitutional purposes where he has a rational and factual understanding of the nature and object of the proceedings against him, has the ability to consult with his lawyer, and has the ability to assist in preparing his defense. Drope v. Missouri, 420 U.S. 162, 171 (1975). Although no particular facts necessarily signal a defendant's incompetence, "evidence of a defendant's irrational behavior, his demeanor at trial, and any prior medical opinion on competence to stand trial are all relevant in determining whether further inquiry is required," and "one of these factors standing alone may, in some circumstances, be sufficient." Drope, 420 U.S. at 180. In addition, a state trial or appellate court's finding that no competency hearing was required is a factual determination entitled to deference unless it is unreasonable within the meaning of 2254(d)(2). Mendez v. Knowles, 556 F.3d 757, 771 (9th Cir.2009); Davis v. Woodford, 384 F.3d at 644.