What is the material change test for a parenting agreement?

Citing ¶114 of L’Heureux-Dubé J.’s concurring opinion in Gordon v. Goertz, (1996) 1996 CanLII 191 (SCC), 134 D.L.R. (4th) 321 (S.C.C.), Kiteley J. wrote, “it is sound public policy that parenting agreements be encouraged. If the contents were simply ignored, it would eliminate any incentive to use the time and resources to negotiate them.” While Kiteley J. went on to expressly apply a material change test, I note that appears to have been based, at least in part, on a submission from counsel that that was the proper approach.