What is the test for exclusive possession of the premises?

"(E)xclusive possession of the premises is not required, nor is physical possession of the narcotic. (Citations.) Although proof of opportunity of access to a place where narcotics are found, without more, will not support a finding of unlawful possession (citation), possession may be imputed where the contraband is found in a location which is subject to joint dominion and control of the accused and another. (Citations.)" (People v. Kanos (1971) 14 Cal.App.3d 642, 652, 92 Cal.Rptr. 614, 619.)