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

A jury verdict in a criminal case must be unanimous. (People v. Russo (2001) 25 Cal.4th 1124, 1132 (Russo).) That is, "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. [Citations.]" (Ibid., original italics.)