What is the test for an allegation of lack of capacity to challenge the validity of a will?

In Ostrander v. Black, [1996] O.J. No. 1372, Grainger J. pointed out that a mere allegation of lack of capacity of a testator is not sufficient to defeat the presumption of knowledge and approval of the contents of a will and testamentary capacity once it is established that the testator read over the will, appeared to understand it, signed it, and the signing was attested to by witnesses, and the formalities of the Succession Law Reform Act were complied with. Under such circumstances the attacker of the will must establish an evidentiary foundation that supports the theory that the testator lacked capacity or did not approve or understand the contents of the will.