Testamentary capacity is a person’s ability or inability to make a Will. It can’t be a valid Will if the will maker doesn’t meet the legal threshold to create a Will in the first place, even if the Will meets the other requisite formalities. https://onyxlaw.ca/reasons-to-contest-a-will-in-bc/ If a Will is declared invalid because of lack of appropriate capacity, the deceased’s next most recent valid Will (if one exists) governs how the deceased’s estate is distributed.
It’s important to emphasize that testamentary capacity is not the same thing as the capacity to manage one’s property or the capacity to grant a power of attorney. A person can have sufficient mental capacity to make a Will even if his or her ability to manage other affairs is impaired. An individual may have a “sound disposing mind” to make a valid BC Will despite the presence of cognitive deterioration or isolated memory deficits. https://onyxlaw.ca/court-affirms-test-for-testamentary-capacity-in-bc-will-challenge/