What is the test for determining whether provocation can negate deliberation and premeditation?

The test for determining whether provocation can negate deliberation and premeditation is a subjective test. "The issue is whether the provocation precluded the defendant from deliberating. [Citation.] This requires a determination of the defendant's subjective state. The court in People v. Wickersham (1982) 32 Cal.3d 307 [overruled on another ground in People v. Barton (1995) 12 Cal.4th 186, 201], impliedly referred to a subjective test: '[W]here the evidence of provocation would justify a jury determination that the accused had formed the intent to kill as a direct response to the provocation and had acted immediately, the trial court is required to give instructions on second degree murder under this theory. The fact that heated words were exchanged or a physical struggle took place between the victim and the accused before the fatality may be sufficient to raise a reasonable doubt in the minds of the jurors regarding whether the accused planned the killing in advance.' (Wickersham, supra, at p. 329.)" (People v. Fitzpatrick (1992) 2 Cal.App.4th 1285, 1295-1296.)