What is the test for allowing a witness to testify in a sexual assault case?

As noted above, a witness must be allowed to testify unless he or she (1) cannot communicate intelligibly, (2) cannot understand the duty of truthful testimony, or (3) lacks personal knowledge of the events to be recounted. But while the first two questions are determined entirely by the court, its role with respect to the issue of personal knowledge is more limited. A witness challenged for lack of personal knowledge must nonetheless be allowed to testify if there is evidence from which a rational trier of fact could find that the witness accurately perceived and recollected the testimonial events. Once that threshold is passed, it is for the jury to decide whether the witness's perceptions and recollections are credible. (See People v. Dennis (1998) 17 Cal.4th 468, 525-526, 71 Cal.Rptr.2d 680, 950 P.2d 1035 (Dennis.))