Bull v Fulton (1942) 66 CLR 295

This case is the leading Australian authority on insane delusions and the effect they have on the validity of a will.  This case considered whether or not a will was valid in the light of overwhelming evidence that a deceased was wrong in their accusations against the propounders of the will.  The onus of proof is upon the person propounding the will.  Nevertheless the delusions ultimately made the will invalid.