What is the test to assess credibility of witnesses?

59 The test to assess the witnesses’ credibility is set out in Faryna v. Chorney, 1951 CanLII 252 (BC CA), [1952] 2 D.L.R. 354 (B.C.C.A) as follows: 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 in 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. … (at p. 357)