What is the threshold test for variation of a support order?

In the case of Willick v. Willick (1994), 1994 CanLII 28 (SCC), 6 R.F.L. (4th) 161 (S.C.C.) the court set out what has been described as the "threshold test" to be applied in the case of applications to vary support orders. At para. 21, pp. 179-180, Sopinka, J. stated: 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...