What is the test for excluding an eyewitness identification of a defendant in a sexual assault case?

"When an eyewitness identification of the defendant is a key element of the prosecution's case but is not substantially corroborated by evidence giving it independent reliability, and the defendant offers qualified expert testimony on specific psychological factors shown by the record that could have affected the accuracy of the identification but are not likely to be fully known to or understood by the jury, it will ordinarily be error to exclude that testimony." (People v. McDonald, supra, 37 Cal.3d at p. 377, fn. omitted, 208 Cal.Rptr. 236, 690 P.2d 709.)