twoFreshStoresDoNotShareState

The fixture precondition the rest of this file rests on: newStore hands back a store that shares no medium with the last one.

Every absence assertion in this suite — readOfANeverWrittenKeyIsNull, deleteOfAnAbsentKeyIsANoOp, the deleted-key half of deleteMakesTheKeyAbsentAndWritableAgain — is a claim about a fresh store. Against a subclass returning one shared instance those assertions would be reporting on whatever an earlier test left behind, and since tests run in an unspecified order the suite would be green or red by accident. This is the property that makes the fixture prove itself rather than being taken on trust.

Deliberately not implied by restart: that hook exists to return a store that does share the medium, so the two hooks are asserting opposite things and neither substitutes for the other.