What is the legal test for a will of an elderly woman with dementia?

This case is an example of the difficulty faced by a solicitor when taking instructions for a will from an elderly person with diminished mental powers. As noted in Leger v. Poirier, a solicitor may be confronted by the situation of testamentary incapacity accompanied by a deceptive ability to answer questions about ordinary and usual matters. The problem is exacerbated where the solicitor has minimal or no familiarity with the testator in her previous life, or of her present medical condition.