Depends on your language for ressources and what you are looking for. Unit testing is supposed to test the code alone with no external dependecy (db, API,...),

Depends on your language for ressources and what you are looking for. Unit testing is supposed to test the code alone with no external dependecy (db, API,...), that's when you need mocks/stubs. Unit testing helps a lot with refactoring and code quality. Integration tests are here to ensure your app/module will work fine once deployed. I don't have any particular recommendation for a site or else, I think the best is to do some research, make up your own mind and see what suits best your case/needs.