Most of the time for third-party services, I'll just fake the service client for unit tests. For example, if I'm writing a BookStoreApp that has a BookStore dependency (where BookStore is an interface), the concrete implementation for which is a PostgresBookStore, then I'll write my PostgresBookStore client library with unit tests that include a real postgres connection but then my BookStoreApp tests will use a FakeBookStore (which is probably a thin wrapper around a dict, but which behaves like a BookStore should modulo persistence). Finally, I'll have considerably fewer API tests which actually do stand up the complete backend service (including a PostgresBookStore). This way I get a high degree of confidence and also speed of test execution--it's also nice not to have to stand up the entire world just to run one test (in particular, it's nice not to have to debug unrelated connection/auth issues).
Re:Don’t mock what you don’t own
by throwaway894345 on Wednesday June 22, 2022 @03:40PM
(#31840859)
I like to distinguish between mocks and fakes. Mocks just return whatever you tell them to return for that test, but a fake is a simplified in-memory implementation (fakes aren't useful for testing error conditions, however, so you may need a few tests which actually do mock if you want to get more complete coverage).
At at an earlier company, we had very little patching or mocking. We spun up all the internal services when running the tests. Internal calls were never mocked. External calls were sometimes mocked (if test accounts / API keys were not convenient.) We preferred testing the "real thing." Tests ran slower but in general I had much more confidence tests actually did something useful.