Art. 28.12. EXCEPTION AND TRIAL OF SPECIAL PLEAS.  When a special plea is filed by the defendant, the State may except to it for substantial defects.  If the exception be sustained, the plea may be amended.  If the plea be not excepted to, it shall be considered that issue has been taken upon the same.  Such special pleas as set forth matter of fact proper to be tried by a jury shall be submitted and tried with a plea of not guilty.
Acts 1965, 59th Leg., p. 317, ch. 722, Sec. 1, eff. Jan. 1, 1966.