What is the test for pleading not guilty by reason of insanity in a criminal case?

For example, in People v. Villarreal (1985) 167 Cal.App.3d 450, 213 Cal.Rptr. 179, the defendant pled not guilty by reason of insanity to a murder charge in 1976. He waived his right to jury trial and stipulated that the court could decide the issue on written reports and the transcript of the preliminary hearing. The court found him not guilty by reason of insanity and ordered him committed to a state hospital until he could prove restoration of sanity. Seven years later, when the district attorney moved to set a [2 Cal.App.4th 1354] trial date to determine the degree of the murder, the trial court denied defendant's request for a jury trial. On appeal he contended he was deprived of his right to jury trial on the issue of degree. The reviewing court responded: "Not so. He waived it in 1976. Trying the issue of alleged insanity of a person who is charged with a crime is not a separate trial, but merely a separate determination of one of the issues of the original charge. [Citations.] In the eyes of the law there is only one trial even though it is divided into two sections or states if insanity is pleaded as a defense. [Citation.]" (167 Cal.App.3d at p. 458, 213 Cal.Rptr. 179, original emphasis.)