What is the test for credibility in a criminal case?

In my assessment of the evidence, I apply the well-established principles as articulated in Faryna v. Chorny, 1951 CanLII 252 (BC CA), [1952] 2 D.L.R. 354 (BCCA) at paras. 10-11: (…) Opportunities for knowledge, powers of observation, judgment and memory, ability to describe clearly what he has seen and heard, as well as other factors, combine to produce what is called credibility… 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 carries 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. (…)