What is the test for assisting and abetting a person in the possession of a Class A drug?

2 'The possession [of narcotics] may be individual, through an agent, or joint with another. People v. Graves, 84 Cal.App.2d 531, 534, 191 P.2d 32. All persons concerned in the commission of the crime, whether they commit the act constituting the offense or aid and abet in its commission, are principals. Pen.Code, 31. We think it clear that one may aid and abet another in the possession of a narcotic * * *.' People v. Bigelow, 104 Cal.App.2d 380, at page 389, 231 P.2d 881, at page 887.