Is it okay for me to take my daily allegra (fexofenadine) allergy pill before a test?

Yes: Fexofenadine, or Allegra (fexofenadine) has no effect on the central nervous system or brain, even at high doses. There should be no sedation or impairment of your ability to take the exam. An interesting controlled study from the netherlands several years ago did show, however, that non-allergic students did better than allergic students even with treatment with clartin, a non-sedating antihistamiine. So study!