What is the test for credibility in the context of a finding of self-defense?

An appellate court may not substitute its determination of witness credibility for that of the trier of fact. (People v. Snow (2003) 30 Cal.4th 43, 66.)

The court in People v. Clark (1982) 130 Cal.App.3d 371, overruled on another ground in People v. Blakeley (2000) 23 Cal.4th 82, 92, distilled the following rule from the existing decisional law: "[W]here the evidence is uncontroverted and establishes all of the elements for a finding of self-defense it may be held as a matter of law that the killing was justified; however, where some of the evidence tends to show a situation in which a killing may not be justified then the issue is a question of fact for the [finder of fact] to determine. (People v. Acosta (1955) 45 Cal.2d 538, 542.) Where the evidence is uncontroverted, but reasonable persons could differ on whether the resort to force was justified or whether the force resorted to was excessive, then the issue is a question of fact for the trier of fact. [Citations.]" (People v. Clark, supra, 130 Cal.App.3d at p. 379.)