Tex. Code Crim. Proc. art. 35.07

Each party may challenge the array only on the ground that the officer summoning the jury has wilfully summoned jurors with a view to securing a conviction or an acquittal. All such challenges must be in writing setting forth distinctly the grounds of such challenge. When made by the defendant, it must be supported by his affidavit or the affidavit of any credible person. When such challenge is made, the judge shall hear evidence and decide without delay whether or not the challenge shall be sustained.