[mattgreenrocks]

IMO, it's less about the type of test and more about your ability to get in and test as many code paths as you can of features that your users perceive as critical.

Sometimes that requires E2E tests, sometimes that's integration or unit tests.

My preference is to use something like functional core/imperative shell as much as possible, but the more external dependencies you have the more work you have to do to create an isolated environment free of IO. Not saying it isn't worthwhile, but sometimes it's easier to simply just accept that the tests will be slower due to relying on real endpoints and move on. After all, tests should support velocity, not be an end in and of themselves.