What is the test for provocation in a murder case?

"'It is left to the jury to say whether the evidence is sufficient to lead them to believe, or to entertain a reasonable doubt whether the offense was committed under heat of passion. . . .' 'The sufficiency of provocation to reduce a homicide from murder to manslaughter, and whether defendant did in fact act under such provocation, are questions of fact for the jury.' [Citation.]" (People v. Wells (1938) 10 Cal.2d 610, 623 [overruled on other ground by People v. Holt (1944) 25 Cal.2d 59]; see also People v. Wright (2015) 242 Cal.App.4th 1461, 1494 ["The existence of provocation and its extent and effect, if any, upon the mind of defendant in relation to premeditation and deliberation in forming the specific intent to kill, as well as in regard to the existence of malice [citation], constitute questions of fact for the jury"].)