I did a free antigen test in Germany in one of the test centers before leaving, being careful to ask them to give the result in English. Then I did a test every 2 days, carefully calculating the timing so as to have maximum length of validity for the flights and hotels. So I ended up doing 2 tests at Lisbon airport (€25 X 2) and one at Krakow airport (€36). You also have to remember to complete a passenger locater form to enter each country, which I always did within 24 hours of getting the flights just in case something went wrong. With all that, everything went entirely smoothly.