Here's a simple scenario: a REST API of which you launch multiple, load-balanced replicas of the same service with Gunicorn. Unit and integration tests are run in single-instance cases, but how can you run integration tests that include all instances so you check that they have a single source of truth?
I can think of several ways but I don't know if there's a better one in Python (or in other languages). Maybe I just miss the vocabulary to search for it. Here's what I think
Launching the several instances of the server from some external program, and use API requests from the test to check that.
Use Gunicorn as a module, write a script that works in the same way as the command you used, and run integration tests on that one.
Is there any better way to do this?