What is the test for establishing an agency relationship between a principal and an agent?

and subject to his control, and consent by the other so to act." [Citation.] "The principal must in some manner indicate that the agent is to act for him, and the agent must act or agree to act on his behalf and subject to his control." [Citation.]' [Citations.] Thus, the 'formation of an agency relationship is a bilateral matter. Words or conduct by both principal and agent are necessary to create the relationship . . . .' [Citation.]" (Van't Rood v. County of Santa Clara (2003) 113 Cal.App.4th 549, 571 (Van't Rood).)