What is the test for credibility in a sexual assault case?

In François, McLachlin J., at pp. 836-837, accepted that review for credibility “may involve consideration of the basis for conclusions which the witness has drawn”. A circumstance of poor vantage point indicating unreliable identification, for example, may be less problematic than a challenge to credibility based on the witness’ alleged lack of truthfulness and sincerity. McLachlin J. explained how juries might deal with inconsistencies: … The reasoning here is that the witness may not have been telling the truth for a variety of reasons, whether because of inconsistencies in the witness's stories at different times, because certain facts may have been suggested to her, or because she may have had reason to concoct her accusations. In the end, the jury must decide whether, despite such factors, it believes the witness's story, in whole or in part. That determination turns not only upon such factors as the assessment of the significance of any alleged inconsistencies or motives for concoction, which may be susceptible of reasoned review by a court of appeal, but on the demeanour of the witness and the common sense of the jury, which cannot be assessed by the court of appeal… In considering the reasonableness of the jury's verdict, the court of appeal must also keep in mind the fact that the jury may reasonably and lawfully deal with inconsistencies and motive to concoct, in a variety of ways. The jury may reject the witness's evidence in its entirety. Or the jury may accept the witness's explanations for the apparent inconsistencies and the witness's denial that her testimony was provoked by improper pressures or from improper motives. Finally, the jury may accept some of the witness's evidence while rejecting other parts of it; juries are routinely charged that they may accept all of the evidence, some of the evidence, or none of the evidence of each witness. It follows that we cannot infer from the mere presence of contradictory details or motives to concoct that the jury's verdict is unreasonable. A verdict of guilty based on such evidence may very well be both reasonable and lawful. McLachlin J. cautioned that appellate courts reviewing for unreasonableness must keep in mind that the jury may bring to the difficult business of determining where the truth lies special qualities which appellate courts may not share. This is particularly true of sexual offences where the examination turns on an infinite number of small details related to the credibility of the witnesses, the community in which the actors and the jurors live, the standards of conduct in that area, and so forth: Warkentin v. The Queen, 1976 CanLII 190 (SCC), [1977] 2 S.C.R. 355, at p. 381.