Upvote:2
You need a supervised test.
If you already are in Italy you can have one in many pharmacys in the territory for 15€, but consider a phone call for be sure the pharmacy does the test (many do, but not all...) and also consider booking the test for avoid queue and for be sure they do it at the time you need it (sometimes they do the tests only in the morning for example).
If you do the test abroad and plan to use it in Italy, you need a paper with the result. For the rapid antigen tests the issuer must follow the guidelines and use a test authorized from the EU commission (here the EU commission references). If you do the test in an EU country and the test is valid for that country, i guess there will be no problems.