- Interrupt it: reload, hit back, let the login expire. It should keep the user's progress.
- Repeat it: double-click, open two tabs. It should run once.
- Feed it bad input: the wrong file, a huge one, an empty one. It should say what's wrong and how to fix it.
- Change who or where: a different role, a phone, no internet. It should show only what that user can do, with a way back.