What is the test for imperfect self-defense?

"'"Under the doctrine of imperfect self-defense, when the trier of fact finds that a defendant killed another person because the defendant actually, but unreasonably, believed he was in imminent danger of death or great bodily injury, the defendant is deemed to have acted without malice and thus can be convicted of no crime greater than voluntary manslaughter." [Citation.] . . . [I]mperfect self-defense is not an affirmative defense, but a description of one type of voluntary manslaughter. Thus the trial court must instruct on this doctrine, whether or not instructions are requested by counsel, whenever there is evidence substantial enough to merit consideration by the jury that under this doctrine the defendant is guilty of voluntary manslaughter. [Citation.] If it were a true affirmative defense, however, an instruction would be required only if it appears that the defendant was relying on the defense, or that there was substantial evidence supportive of the defense, and the defense was not inconsistent with the defendant's theory of the case. [Citations.]' [Citation.]" (People v. Manriquez (2005) 37 Cal.4th 547, 581.)