What is the test for determining credibility of a witness?

60. In this case, the Hearing Officer articulates the proper approach to the determination of credibility by referring to the test commonly known as the “O’Hallaran test” which is described in Faryna v. Chorny (1952) 2 D.L.R. (B.C.C.A.): The credibility of interested witnesses, particularly in a case of conflict in evidence must be reasonably subjected to an examination of the consistency of their stories with the possibilities that surround the currently exiting conditions. In short, the real test of the truth of the story of a witness in such cases must be its harmony with the preponderance of the probabilities, which a practical and informed person would readily recognize as reasonable in that place under those conditions. [emphasis added]