2009 California Evidence Code - Section 870 :: Article 3. Opinion Testimony On Particular Subjects

870.  A witness may state his opinion as to the sanity of a person
when:
   (a) The witness is an intimate acquaintance of the person whose
sanity is in question;
   (b) The witness was a subscribing witness to a writing, the
validity of which is in dispute, signed by the person whose sanity is
in question and the opinion relates to the sanity of such person at
the time the writing was signed; or
   (c) The witness is qualified under Section 800 or 801 to testify
in the form of an opinion.