(a) Testamentary capacity exists when the testator has a decided and rational desire as to the disposition of property.
(b) An incapacity to contract may coexist with the capacity to make a will.
(c) An insane individual generally may not make a will except during a lucid interval. Amonomaniac may make a will if the will is in no way connected with the monomania. In all such cases, it must appear that the will expresses the wishes of the testator unbiased by the insanity or monomania with which the testator is affected.
(d) Neither advancing age nor weakness of intellect nor eccentricity of habit or thought is inconsistent with the capacity to make a will.