There are two tests for carbon dioxide:
1. It will extinguish a flame. HOWEVER, as any oxygen free gas will also extinguish a flame this is a poor gas test and may result in misidentification.
2. Bubble it through lime water: A positive test will result in the lime water turning milky.
Lime water turns milky as the Calcium hydroxide (chemical name for limewater) reacts with carbon dioxide to form Calcium Carbonate which is insoluble in water and thus forms a milky white precipitate.
Hope this helps