Infectious disease experts are now saying that fully vaccinated people can gather for the holidays with minimal risk. Testing in advance adds assurance that someone in the group is not unknowingly infected with COVID and thus capable of spreading the virus. When the gathering includes elderly, pregnant, immunocompromised, or unvaccinated people (eg, children under age 5) or partially vaccinated people (eg, children ages 5-11), testing for COVID before gathering becomes more important. It will be necessary to make appointments well in advance if you plan to use a pharmacy for testing. Home antigen tests are now available in some pharmacies and big box stores, to keep on hand for the times they are needed. Masking when indoors adds another layer of protection to any gathering (though of course is impossible during a meal). See also these NYT articles:
https://www.nytimes.com/2021/11/12/briefing/when-will-covid-end.html and
https://www.nytimes.com/2021/11/15/briefing/travel-coronavirus-holidays-thanksgiving.html