What is the test for a testamentary capacity?

The test to be applied when considering testamentary capacity is as set out in Banks v. Goodfellow (1870), 5 Q.B. 549 at 565, by Cockburn C.J.: It is essential to the exercise of such a power that a testator shall understand the nature of the act and its effects; shall understand the extent of the property of which he is disposing; shall be able to comprehend and appreciate the claims to which he ought to give effect; and, with a view to the latter object, that no disorder of the mind shall poison his affections, pervert his sense of right, or prevent the exercise of his natural faculties -that no insane delusion shall influence his will in disposing of his property and bring about a disposal of it which, if the mind had been sound, would not have been made.