What is the test for introducing prior testimony in a personal injury case?

"Under California law, prior testimony may be introduced if, among other things, the declarant is unavailable as a witness. (Evid. Code, 1291.) Unavailability may be established by showing that the declarant is 'Absent from the hearing and the proponent of the statement has exercised reasonable diligence but has been unable to procure his attendance by the court's process.' ( 240, subd. (a)(5).)" (People v. Jackson, supra, 28 Cal.3d 264, 311-312, 168 Cal.Rptr. 603, 618 P.2d 149.)