What is the test for making a threat under section 422 of the California Penal Code?

threat, even if there is no intent of actually carrying it out, which, on its face and under the circumstances in which it is made, is so unequivocal, unconditional, immediate, and specific as to convey to the person threatened, a gravity of purpose and an immediate prospect of execution of the threat, and thereby causes that person reasonably to be in sustained fear for his or her own safety." (Pen. Code, 422, subd. (a).) "In determining whether conditional, vague, or ambiguous language constitutes a violation of [Penal Code] section 422, the trier of fact may consider 'the defendant's mannerisms, affect, and actions involved in making the threat as well as subsequent actions taken by the defendant.' " (People v. Wilson (2010) 186 Cal.App.4th 789, 808.)