What is the test for establishing that a will has been established that the propounder has knowledge and approval?

It is well established that there is a presumption of testamentary capacity. However, as Justice Sopinka stated in Vout v. Hay, 1995 CanLII 105 (SCC), [1995] 2 S.C.R. 876 (S.C.C.) at paragraph 27: Where suspicious circumstances are present, then the presumption [of testamentary capacity] is spent and the propounder of the will reassumes the legal burden of proving knowledge and approval. In addition, if the suspicious circumstances relate to mental capacity, the propounder of the will reassumes the legal burden of establishing testamentary capacity. Both of these issues must be proved in accordance with the civil standard. There is nothing mysterious about the role of suspicious circumstances in this respect. The presumption simply casts an evidentiary burden on those attacking the will. This burden can be satisfied by adducing or pointing to some evidence which, if accepted, would tend to negative knowledge and approval or testamentary capacity. In this event, the legal burden reverts to the propounder.