Rationale
A case that runs against the checkout it lives in changes the state it is testing; test/run.sh creates a fresh repository per case for that reason.
Required behaviour
Behavioural cases run through bash test/run.sh in a temporary repository each, never against this checkout.
Failure behaviour
No command decides this rule; a reviewer does, and a change that violates it is not merged. Where a behavioural case covers part of it, that case is named below.
Verification
Review. test/run.sh; a case that writes into ROOT is a bug the derived-artifacts case would report.