What is the test for determining the validity of a will?

Testamentary capacity is a question of fact to be determined by examining all relevant circumstances. A testator is presumed to have capacity, unless a party raises a genuine issue, in which case, capacity must be proven on a balance of probabilities to establish the validity of a will: O’Neil v. Royal Trust Co., 1946 CanLII 13 (SCC), [1946] S.C.R. 622, at para. 32.

Where suspicious circumstances surrounding the preparation of the will exist, the presumption of capacity is no longer in effect, and the party seeking to prove the will must establish that the deceased had knowledge of and approved of the contents of the will, and had testamentary capacity. Vout v. Hay 1995 CanLII 105 (SCC), [1995] 2 SCR 876 at 888.