What is the test for giving a jury a unanimous verdict in a sexual assault case?

"Under Chapman, 'where the record provides no rational basis, by way of argument or evidence, for the jury to distinguish between the various acts, and the jury must have believed beyond a reasonable doubt that [the] defendant committed all acts if he committed any, the failure to give a unanimity instruction is harmless.' [Citation.] For example, where the defendant offered the same defense to all criminal acts and 'the jury's verdict implies that it did not believe the only defense offered,' failure to give a unanimity instruction is harmless error. [Citation.] . . . The error is also harmless '[w]here the record indicates the jury resolved the basic credibility dispute against the defendant and therefore would have convicted him of any of the various offenses shown by the evidence. . . .' [Citation.]" (People v. Hernandez, supra, 217 Cal.App.4th at p. 577.)