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

No better statement exists in our jurisprudence than that of O’Halloran J.A. in Faryna v. Chorny, 1951 CanLII 252 (BC CA), [1952] 2 D.L.R. 354, where his Lordship, at p. 356, said this: The credibility of interested witnesses, particularly in cases of conflict of evidence, cannot be gauged solely by the test of whether the personal demeanour of the particular witness carried conviction of the truth. The test must reasonably subject his story to an examination of its consistency with the probabilities that surround the currently existing conditions. In short, the real test of the truth of the story of a witness in such a case must be its harmony with the preponderance of the probabilities which a practical and informed person would readily recognize as reasonable in that place and those conditions. Only thus can a Court satisfactorily appraise the testimony of quick-minded, experienced and confident witnesses, and of those shrewd persons adept in the half-lie and of long and successful experience in combining skilful exaggeration with partial suppression of the truth. Again a witness may testify what he sincerely believes to be true, but he may be quite honestly mistaken. For a trial Judge to say “I believe him because I judge him to be telling the truth”, is to come to a conclusion on consideration of only half the problem. In truth it may easily be self-direction of a dangerous kind. The trial Judge ought to go further and say that evidence of the witness he believes is in accordance with the preponderance of probabilities in the case and, if his view is to command confidence, also state his reasons for that conclusion. The law does not clothe the trial Judge with a divine insight into the hearts and minds of the witnesses. . . .