What is the test for establishing a conspiracy?

"[A] conspiracy may be established by direct evidence or circumstantial evidence, or a combination of both. It need not be shown that the parties entered into a definite agreement, but it is sufficient if they positively or tacitly come to a mutual understanding to accomplish the act and unlawful design." (People v. Calhoun (1958) 50 Cal.2d 137, 144; see also People v. Zamora (1976) 18 Cal.3d 538, 559 [noting "the well established rule that the unlawful design of a conspiracy may be proved by circumstantial evidence without the necessity of showing that the conspirators met and actually agreed to commit the offense which was the object of the conspiracy"].) "It is, of course, unnecessary that each conspirator see the others or know who all the members of the conspiracy are. [Citations.] [] It is likewise

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unnecessary that each conspirator participate in the overt acts. [Citations.]" (People v. Buffum (1953) 40 Cal.2d 709, 725, disapproved on other grounds in People v. Morante (1999) 20 Cal.4th 403, 430.)

"[W]here a person joins a conspiracy after its formation and actively participates in it, he adopts the prior acts and declarations of his fellow conspirators pursuant to the conspiracy to the extent that evidence of those acts and declarations is admissible against him. [Citations.] And . . . it is admissible against him only to show such matters as the nature and objectives of the conspiracy in which he joins, and the incidents thereof, but not to prove his guilt of substantive crimes theretofore committed." (People v. Weiss (1958) 50 Cal.2d 535, 565, disapproved on other grounds in People v. Johnson (1980) 26 Cal.3d 557, 570-571.)