Even if it's not signed by two witnesses (as required by the Probate Code), if you dictate a will to someone, they write it down, you sign it, and several people see you do all this, that's enough for a valid will. So holds the Court of Appeal.
Now, admittedly, in the present case, the testator did something else as well. In front of the witnesses, he also got out a copy of his old will, urinated on it, and burned it.
But I'm pretty sure that's optional.