I think you have no claim here. I am fairly sure what TAP are doing is not against the law, as I don't think there is a law saying passengers specifically do NOT need a COVID-19 test. Also I guess there might be a law or regulation saying passengers must be medically fit before flying.

If I was in your position I would try to take the flight, and if refused boarding take a test and a later flight. Chalk it up as the result of travelling during a pandemic with lots of fast changing restrictions.