What is the legal test for the doctrine of undue influence over the execution of a will?

Evidence of undue influence may also trigger the doctrine of suspicious circumstances. Upon proof that the will was duly executed with the requisite formalities, it will generally be presumed that the testator knew and approved of the contents and had the necessary testamentary capacity. Where, however, suspicious circumstances are present i.e., there is evidence which if accepted would tend to negative knowledge and approval or testamentary capacity, then the presumption is spent and the propounder of the will reassumes the burden of proving knowledge and approval of the contents of the will. In addition, if suspicious circumstances relates to mental capacity, the propounder of the will reassumes the legal burden of establishing testamentary capacity. Vout v. Hay 1995 CanLII 105 (SCC), [1995] 2 SCR 876.