755 ILCS 5/6-17

Witness to appear for probate - penalty.) It is the duty of a witness to any will executed in this State to appear before the court at the hearing on the admission of the will to probate and testify concerning the execution and validity of the will unless proof of will is made by another method as provided in this Act. The court may attach and punish by fine and imprisonment, or either, any witness who, without a reasonable excuse, fails to appear and testify when subpoenaed.