[haroldl]

One reason for tests to hit a real external API is if you're using a "record and replay" test framework to capture the interactions so that you can run the tests against the recorded data quickly later. But because the API calls you make change (and the external implementation changes) you need to re-record from time to time.

This strikes a balance where 99% of the time you are making calls that never leave the process for fast testing, but can validate against the real implementation as needed.