W. Va. Code § 56-4-22

Upon the plea mentioned in the next preceding section, the plaintiff may join issue without other pleading. But if the plaintiff intends to rely upon any matter in waiver, estoppel, or in confession and avoidance of any matter which may have been stated by the defendant as aforesaid, the plaintiff must file a statement in writing, specifying in general terms the matter on which he intends so to rely; and such statement must be verified by the oath of the plaintiff, or some other credible person, to the effect that the affiant believes the matter of reply therein stated will be supported by evidence at the trial.