What is the test for certifying an action on the basis of common law issues?

As noted per McLachlin C.J.C. in Hollick v. Toronto (City), [2001] 3 S.C.R. 158, 2001 SCC 68, at para. 18: 18 ... As I wrote in Western Canadian Shopping Centres, the underlying question is “whether allowing the suit to proceed as a representative one will avoid duplication of fact-finding or legal analysis”. Thus an issue will be common “only where its resolution is necessary to the resolution of each class member’s claim” (para. 39). Further, an issue will not be “common” in the requisite sense unless the issue is a “substantial ... ingredient” of each of the class members’ claims. Earlier, in Rumley v. British Columbia, [2001] 3 S.C.R. 184, 2001 SCC 69, at para. 29, it was noted “... It would not serve the ends of either fairness or efficiency to certify an action on the basis of issues that are common only when stated in the most general terms. ...”