[backendscheduler] test: cover that measureTenants keeps the outstanding-blocks gauge alive during redaction - #7716
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… a redaction The measurement selector that keeps compaction_outstanding_blocks reporting real work while a tenant's compaction is gated (grafana#6992) had a unit test, but nothing asserted measureTenants actually used it — swapping the call back to the TenantPending-guarded selector left the whole suite green. Since the worker autoscaler scales on that gauge, the regression would scale workers down underneath a running redaction and only surface as the redaction getting slower. This asserts the gauge itself after measureTenants, so the wiring is covered rather than just the selector, and narrows the older test's comment to what it actually checks.
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What this PR does:
Adds the missing coverage for a fix that was silently unprotected.
compaction_outstanding_blocksmust keep reporting real work while a tenant's compaction is gated by a redaction batch — the worker autoscaler scales on that gauge, so a zero reading scales workers down underneath a running redaction and only surfaces as the redaction getting slower the longer it runs. That was fixed in #6992 by givingmeasureTenantsits own selector (newBlockSelectorForMeasurement) that skips theTenantPendingguard.The selector had a unit test. Nothing asserted that
measureTenantsactually used it: swapping the call back to the gatednewBlockSelectorleaves the entire suite green, so the regression could return unnoticed.This adds
TestCompactionProvider_MeasureTenantsPublishesBlocksDuringRedaction, which callsmeasureTenants()with a gated tenant and asserts the gauge itself is non-zero — covering the wiring rather than just the selector. Verified by mutation: green as-is, red when the call is swapped back.Also narrows the existing test's comment, which claimed it ensured "the outstanding-blocks metric (and therefore autoscaling) is not disrupted" while never touching the metric or the caller.
Test-only; no production change.
Which issue(s) this PR fixes:
N/A — follow-up coverage for #6992.
Checklist
.chloggen/(test-only, no user-facing change)