* test: restore maintenance mode coverage in TestVolumeMarkReadonlyWritableErrorPaths
PR #8360 removed the maintenance mode assertions because the refactored
check ordering (volume lookup before maintenance check) caused the
original test to hit "not found" instead of "maintenance mode" — the
test used a non-existent volume ID.
Restore coverage by allocating a real volume, then verifying:
- existing volume in maintenance mode returns "maintenance mode"
- non-existent volume in maintenance mode still returns "not found"
(validating the new check ordering)
* test: add coverage for ScrubVolume MarkBrokenVolumesReadonly flag
PR #8360 added the mark_broken_volumes_readonly field to ScrubVolumeRequest
but no tests exercised the new logic paths. Add three integration tests:
- HealthyVolume: flag is a no-op when scrub finds no broken volumes
- CorruptVolume: corrupted .idx triggers broken detection; without the
flag the volume stays writable, with the flag it becomes read-only
- MaintenanceMode: makeVolumeReadonly fails under maintenance and
ScrubVolume propagates the error via errors.Join
* refactor: extract CorruptIndexFile and EnableMaintenanceMode test helpers
Move duplicated idx corruption and maintenance mode setup into
framework.CorruptIndexFile() and framework.EnableMaintenanceMode()
helpers. Use defer for file close in the corruption helper.
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