What is the test for determining whether a defendant was sane at the time of the trial?

"On the day set for sentencing, the parties reminded the court that a sanity hearing had not been conducted immediately after the guilt phase, as required by [ ] section 190.1, subdivision (c). Over defendant's objection that the same jury must determine all the issues in a capital trial, the court empaneled a new jury to decide the issue of sanity alone. After deliberations that spanned 11 days the jurors reported they were hopelessly deadlocked, and a mistrial was declared. Over defendant's further objection, the court then called back the original jurors--who had been discharged more than five months earlier--and reempaneled them without examining them itself or allowing voir dire by the parties. This jury returned a verdict that defendant was sane at the time of the crimes charged. Thereupon the court imposed the sentence of death." (People v. Hendricks (1987) 43 Cal.3d 584, 588-589, 238 Cal.Rptr. 66, 737 P.2d 1350.)