Tex. R. Civ. P. 92
A general denial of matters pleaded by the adverse party which are not required to be denied under oath, shall be sufficient to put the same in issue. When the defendant has pleaded a general denial, and the plaintiff shall afterward amend his pleading, such original denial shall be presumed to extend to all matters subsequently set up by the plaintiff.
When a counterclaim or cross-claim is served upon a party who has made an appearance in the action, the party so served, in the absence of a responsive pleading, shall be deemed to have pleaded a general denial of the counterclaim or cross-claim, but the party shall not be deemed to have waived any special appearance or motion to transfer venue. In all other respects the rules prescribed for pleadings of defensive matter are applicable to answers to counterclaims and cross-claims.
Tex. R. Civ. P. 92