What is the test for instructing a jury on a lesser included offense in a sexual assault case?

"A criminal defendant has a constitutional right to have the jury determine every material issue presented by the evidence, and an erroneous failure to instruct on a lesser included offense constitutes a denial of that right. To protect this right and the broader interest of safeguarding the jury's function of ascertaining the truth, a trial court must instruct on an . . . offense that is less serious than, and included in, a . . . greater offense . . . , whenever there is substantial evidence raising a question as to whether all of the elements of the charged greater offense are present." (People v. Huggins (2006) 38 Cal.4th 175, 215.) Thus, " ' "such instructions are required whenever evidence that the

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defendant is guilty only of the lesser offense is 'substantial enough to merit consideration' by the jury. [Citations.] 'Substantial evidence' in this context is ' "evidence from which a jury composed of reasonable [persons] could . . . conclude[ ]" ' that the lesser offense, but not the greater, was committed." ' [Citation.] The classic formulation of this rule is expressed in People v. Webster [1991] 54 Cal.3d 411, 443: 'When there is substantial evidence that an element of the charged offense is missing, but that the accused is guilty of a lesser included offense, the court must instruct upon the lesser included offense. . . .' " (Ibid.)