Just reading the FAQs for Cruises from U.S. & Canada. "Guests on back to back voyages will need to disembark the ship at the end of each voyage, receive a complementary viral Covid-19 tests, and will be permitted to board the ship again once they receive a negative test result."
It goes on to state that, at present, guests will not need to pack and disembark with luggage for this testing between cruises. Final details will be confirmed on board.
I hope it all works out.