Well, that's asking me to disprove a negative. All I can say is that I don't think that principle is true.

One counter-example of a scenario that is impossible to integration test but possible to unit test would be sufficient to disprove my hypothesis, but I don't think it exists and I don't think you can provide it.

>Even if you take every example I give and claim "doesn't count, I'd test for that", you're just writing unit-tests-once-removed using an integration testing framework.

I'm really not. I can test disconnection scenarios in an integration test without even coupling to the language under test by running a service that intercepts network traffic. It's obviously not a "unit test once removed" if I can literally swap out the entire language under test and not have to change the test.