W. Va. Code § 56-5-5
In any action on a contract, the defendant may file a plea alleging any such failure in the consideration of the contract, or fraud in its procurement, or any such breach of any warranty to him of the title to real property or of the title or the soundness of personal property, for the price or value whereof he entered into the contract, or any other matter, as would entitle him either to recover damages at law from the plaintiff, or the person under whom the plaintiff claims, or to relief in equity, in whole or in part, against the obligation of the contract; or, if the contract be by deed, alleging any such matter existing before its execution, or any such mistake therein, or in the execution thereof, or any such other matter, as would entitle him to such relief in equity; and in either case alleging the amount to which he is entitled by reason of the matters contained in the plea. Every such plea shall be verified by affidavit.
W. Va. Code § 56-5-5