What is the test for unlawful homicide in the context of self-defense?

Under principles of self-defense, only that force which is necessary to repel an attack is justified; force which exceeds the necessity is not justified. (People v. Clark (1982) 130 Cal.App.3d 371, 380.) Further, deadly force or force likely to cause great bodily injury may be used only to repel an attack which in itself is deadly or likely to cause great bodily injury. (Ibid.) Under these two principles, a person may be found guilty of unlawful homicide even where the evidence establishes the right to self-defense if the jury finds that the nature of the attack did not justify the resort to deadly force or that the force used exceeded that which was reasonably necessary to repel the attack.