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

"Defendants in criminal cases have a constitutional right to a unanimous jury verdict. [Citation.] From this constitutional principle, courts have derived the requirement that if one criminal act is charged, but the evidence tends to show the commission of more than one such act, 'either the prosecution must elect the specific act relied upon to prove the charge to the jury, or the court must instruct the jury that it must unanimously agree that the defendant committed the same specific criminal act.' [Citations.]" (People v. Napoles (2002) 104 Cal.App.4th 108, 114.) " 'The [unanimity] instruction is 'designed in part to prevent the jury from amalgamating evidence of multiple offenses, no one of which has been proved beyond a reasonable doubt, in order to conclude beyond a reasonable doubt that a defendant must have done something sufficient to convict on one count.' [Citation.]" (People v. Russo (2001) 25 Cal.4th 1124, 1132.)