What is the legal test for an aider and abettor of a murder case?

People v. McCoy, supra, 25 Cal.4th 1111, 1117, explained: "It is important to bear in mind that an aider and abettor's liability for criminal conduct is of two kinds. First, an aider and abettor with the necessary mental state is guilty of the intended crime. Second, under the natural and probable consequences doctrine, an aider and abettor is guilty not only of the intended crime, but also 'for any other offense that was a "natural and probable consequence" of the crime aided and abetted.' (People v. Prettyman, supra, 14 Cal.4th at p. 260.) Thus, for example, if a person aids and abets only an intended assault, but a murder results, that person may be guilty of that murder, even if unintended, if it is a natural and probable consequence of the intended assault. (Id. at p. 267.)"