What is the test for unanimous verdict in a criminal case?

"In a criminal case, a jury verdict must be unanimous." (People v. Russo (2001) 25 Cal.4th 1124, 1132.) "Additionally, the jury must agree unanimously the defendant is guilty of a specific crime. [Citation.] Therefore, cases have long held that when the evidence suggests more than one discrete crime, either the prosecution must elect among the crimes or the court must require the jury to agree on the same criminal act." (Ibid.) "When the prosecutor does not make an election, the trial court has a sua sponte duty to instruct the jury on unanimity." (People v. Mayer (2003) 108 Cal.App.4th 403, 418.)