One of my more favorite forms of testing is offline E2E testing. Python and Go are very adept at doing this kind of testing, which is nice. The idea is that you

One of my more favorite forms of testing is offline E2E testing. Python and Go are very adept at doing this kind of testing, which is nice. The idea is that you use exposed APIs (read: anything for consumption. Could be REST but also could be important packages) just as the user would use them. The nature of testing is that it captures the discreet contracts you're mentioning by reusing the API itself and ensures them. There's a discussion to be had that's the volume of E2E vs unit tests, but that isn't this discussion.