Texas Natural Resources Code - NAT RES § 162.040. Validity of Bonds

(a) After the bonds are approved by the attorney general and registered with the comptroller of public accounts, they shall be held as valid and binding general obligations of the state in every action, suit, or proceeding in which their validity is or may be brought into question.

(b) In each action brought to enforce collection of the bonds or rights incident to the bonds, the certificate of approval by the attorney general or certified copy of that certificate shall be admitted and received in evidence as to the validity of the bonds.

(c) Only forgery or fraud may be offered as a challenge to the validity of the bonds.