> I wouldn't say that isolation and realism are completely orthogonal

Neither would I. I'm arguing that when you write a test method, you deliberately make the choice to include some kind of 'before-all' method, or not.

The reasons you would choose to include a 'before-all' method will vary from case to case. Let's say you're testing an addUser method. If you choose to isolate its state to avoid 'test flakiness', it is you making the call that addUser is flaky when run against shared state.

What is it about your application code that would make you think that addUser is flaky enough to need a clean slate to run against? Why not change the application code instead?