What is the test for reducing first degree murder to second degree manslaughter?

In short, "[t]he test of whether provocation or heat of passion can negate malice so as to mitigate murder to voluntary manslaughter is objective. . . . The test of whether provocation or heat of passion can negate deliberation and premeditation so as to reduce first degree murder to second degree murder, on the other hand, is subjective." (People v. Padilla, supra, 103 Cal.App.4th at p. 678.)

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