fusion/docs/solutions/logic-errors/quarantine-data-file-forces-gate-mode-dropping-coverage.md

title, date, category, module, problem_type, component, symptoms, root_cause, resolution_type, severity, related_components, tags

title	date	category	module	problem_type	component	symptoms	root_cause	resolution_type	severity	related_components	tags
Shared-infra catch-all forces gate mode, silently dropping changed-package coverage	2026-06-19	logic-errors	scripts/test-changed	logic_error	testing_framework	`pnpm test` ran ~700 fixed engine-core + cli-shape tests while the developer's actually-changed packages got zero coverage `node scripts/test-changed.mjs --print-mode` reported `mode=gate reason=shared-infra-changed` on a branch that only touched package source plus a data file Changed packages (@fusion/core, @fusion/dashboard) resolved as affected but never ran	logic_error	code_fix	medium	development_workflow	test-changed gate-mode test-selection affected-packages shared-infra quarantine silent-coverage-loss

Shared-infra catch-all forces gate mode, silently dropping changed-package coverage

Problem

pnpm test (→ scripts/test-changed.mjs) routed to gate mode whenever the diff touched scripts/lib/test-quarantine.json — a runtime data list of quarantined tests, not executable infra. Gate mode runs only the fixed merge-gate slice (pnpm test:gate = engine-core + cli ci-shape) and returns before the affected packages, so a developer who also edited the quarantine list got zero coverage of their real changes.

Symptoms

• pnpm test spent ~22s passing ~700 engine/cli tests unrelated to the change; the changed code never ran.
• --print-mode showed mode=gate reason=shared-infra-changed packages=0 on a branch whose only "infra" file was scripts/lib/test-quarantine.json.
• The affected-package resolver, given the same diff minus the quarantine file, correctly returned [@fusion/core, @fusion/dashboard] — proving the coverage was being dropped, not just unselected.

What Didn't Work

• Assuming the gate suite covers the change — gate mode runs a fixed slice (engine-core + cli ci-workflow shape) regardless of what changed. It is a trust signal, not a coverage signal for arbitrary packages. Reading only the green output hides the gap.
• Blaming the cache — the content-hash cache was a red herring; the run never reached the affected-package path at all because decideExecutionPlan short-circuited to gate first.

Solution

The catch-all in isSharedInfraChange (scripts/test-changed.mjs) treats any changed file outside packages/, plugins/, or docs/ as shared infra. The quarantine data file hit it. Classify it as test-irrelevant in isTestIrrelevantRootPath so the diff stays in changed mode:

// scripts/test-changed.mjs — isTestIrrelevantRootPath
// The quarantine list is runtime DATA (which tests are skipped), not
// executable test infra. Editing it must not trip the root catch-all below
// and force gate mode — gate mode drops affected-package coverage.
if (file === "scripts/lib/test-quarantine.json") {
  return true;
}

After the fix, --print-mode reports mode=changed and the affected packages run again. Regression tests in scripts/__tests__/test-changed.test.mjs assert the quarantine list — alone and alongside package changes — stays in changed mode. Shipped in PR Runfusion/Fusion#1686.

Why This Works

decideExecutionPlan checks isSharedInfraChange(changedFiles) before resolving affected packages, and gate mode is terminal (runMaybeIsolated("test:gate") then return). So the shared-infra signal doesn't augment affected coverage — it replaces it. That tradeoff is defensible for a genuine infra change (you can't trust the affected-resolution when the resolver's own inputs moved), but a quarantine-list edit doesn't invalidate affected resolution; it's just data. Marking it test-irrelevant lets the diff fall through to normal affected-package selection (which still runs the gate first, then the affected set), so the developer's real changes get tested.

Prevention

• Know the replacement semantics: in test-changed, shared-infra/gate mode replaces affected-package coverage rather than adding to it. Any changed file not under packages/, plugins/, or docs/ hits the catch-all and silently drops changed-code testing until it's explicitly allowlisted in isTestIrrelevantRootPath.
• Allowlist new data/config files under scripts/: when adding a runtime data file (JSON lists, fixtures, generated catalogs) that lives outside the package tree, add it to isTestIrrelevantRootPath — or it will force every diff that touches it into gate-only mode.
• Verify mode, not just green: when a test run looks suspiciously fast or generic, run node scripts/test-changed.mjs --print-mode. mode=gate reason=shared-infra-changed packages=0 on a branch with real package changes is the tell that coverage is being dropped.
• Test the coverage invariant, not just the boolean: the regression test asserts a quarantine edit + package change stays in changed mode — i.e. that the affected packages would run, not merely that isSharedInfraChange returns false.

Related Issues

• PR Runfusion/Fusion#1686 — the fix this doc documents
• files-changed-inflated-by-origin-first-base-commit — adjacent test/diff-tooling logic bug in the same scripts/engine tooling family