What is the test for establishing that evidence of a prior sexual assault is indisputably relevant in a prosecution for another sexual offence?

"[E]vidence of a 'prior sexual offense is indisputably relevant in a prosecution for another sexual offense.' [Citation.]" (Branch, supra, 91 Cal.App.4th at pp. 282-283.) "The charged and uncharged crimes need not be sufficiently similar that evidence of the latter would be admissible under Evidence Code section 1101, otherwise Evidence Code section 1108 would serve no purpose. It is enough the charged and uncharged offenses are sex offenses as defined in [Evidence Code] section 1108." (People v. Frazier (2001) 89 Cal.App.4th 30, 40-44 (Frazier), fn. omitted.)