What is the test for issuing a writ of habeas corpus ad testificandum directing the production of an inmate witness for trial?

The court must exercise its discretion to determine whether to issue a writ of habeas corpus ad testificandum directing the production of an inmate witness for trial, based on a consideration of such factors as: (1) whether the prisoner's presence will substantially further the resolution of the case; (2) security risks presented by the prisoner's presence; (3) the expense of the prisoner's transportation and safekeeping; and (4) whether the suit can be stayed until the prisoner is released without prejudice to the cause asserted." Wiggins v. County of Alameda, 717 F.2d 466, 468 n.1 (9th Cir. 1983) (quoting Ballard v. Spradley, 557 F.2d 476, 480 (5th Cir.

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