What is the threshold test for determining whether a change has been made to the terms of a contract?

The threshold test as discussed in Willick v. Willick,1994 CanLII 28 (SCC), [1994] 3 S.C.R. 670, at 688 indicates as follows: “In deciding whether the conditions for variation exist, it is common ground that the change must be a material change of circumstances. This means a change, such that, if known at the time, would likely have resulted in different terms. The corollary to this is that if the matter which is relied on as constituting a change was known at the relevant time it cannot be relied on as the basis for variation.”