What is the test for undue influence of a will?

As noted per Sopinka J. in Vout v. Hay (1995), 1995 CanLII 105 (SCC), 125 D.L.R. (4th) 431 (S.C.C.) at p. 438-39: “undue influence. . . .requires proof that the testator’s assent to the will was obtained by influence such that instead of representing what the testator wanted, the will is a product of coercion. . . .”. Influencing a person to act in a certain manner by providing that person with misinformation is mental coercion, if not also fraud. The person receiving the information is constrained to act contrary to what their free will would normally dictate if he or she had not been subjected to the misinformation.