What is the test for reasonable self-defense in the context of a homicide case?

^4. In the context of homicide crimes, self-defense may be available even where a defendant acts unreasonably. "Self-defense, when based on a reasonable belief that killing is necessary to avert an imminent threat of death or great bodily injury, is a complete justification, and such a killing is not a crime. [Citations.] A killing committed when that belief is unreasonable is not justifiable. Nevertheless, 'one who holds an honest but unreasonable belief in the necessity to defend against imminent peril to life or great bodily injury does not harbor malice and commits no greater offense than manslaughter.' [Citation.]" (People v. Elmore (2014) 59 Cal.4th 121, 134.) "Unreasonable self-defense is 'not a true defense; rather, it is a shorthand description of one form of voluntary manslaughter.' [Citation.] Whenever there is substantial evidence that the defendant killed in unreasonable self-defense, the trial court must instruct on this theory of manslaughter. [Citation.]." (Ibid.) Defendant does not contend that he acted in unreasonable self-defense or that the trial court should have instructed the jury on attempted voluntary manslaughter. We accordingly do not consider the impact, if any, of the absence of these instructions. (See People v. Grimes (2015) 60 Cal.4th 729, 757-758.)