What is the test for unlawful possession of drugs?

'Unlawful possession of narcotics is established by proof (1) that the accused exercised dominion and control over the contraband, (2) that he had knowledge of its presence, and (3) that the accused had knowledge that the material was a narcotic.' (People v. Groom, 60 Cal.2d 694, 696, 36 Cal.Rptr. 327, 329, 388 P.2d 359, 361.) Those elements may be established by circumstantial evidence and inferences. (People v. Groom, supra, at pp. 696--697, 36 Cal.Rptr. 327, 388 P.2d 359.)