What is the test for assessing a child's cognitive development in a sexual assault case?

such factors in evaluating a child's testimony.' [Citation.] . . . 'The instruction tells the jury not to make its credibility determinations solely on the basis of child's 'age and level of cognitive development,' but at the same time invites the jury to take these and all other factors surrounding the child's testimony into account. The instruction provides sound and rational guidance to the jury in assessing the credibility of a class of witnesses as to whom "traditional assumptions" 'may previously have biased the factfinding process. Obviously a criminal defendant is entitled to fairness, but just as obviously he or she cannot complain of an instruction the necessary effect of which is to increase the likelihood of a fair result.' [Citation.]" (People v. McCoy, supra, 133 Cal.App.4th at p. 979.)