What is the test for constructive possession of a firearm?

Possession of a firearm is a general intent crime, and "[p]ossession may be either actual or constructive as long as it is intentional." (People v. Spirlin (2000) 81 Cal.App.4th 119, 130.) "To establish constructive possession, the prosecution must prove a defendant knowingly exercised a right to control the prohibited item, either directly or through another person. [Citations.] Possession may be shared with others. [Citation.] But mere proximity to the weapon, standing alone, is not sufficient evidence of possession." (People v. Sifuentes (2011) 195 Cal.App.4th 1410, 1417 (Sifuentes).)