diff --git a/scripts/__tests__/check-audit.test.mjs b/scripts/__tests__/check-audit.test.mjs
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+++ b/scripts/__tests__/check-audit.test.mjs
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+/**
+ * Unit tests for check-audit.mjs filter logic.
+ *
+ * Tests the four behavioral cases without spawning pnpm:
+ *  1. Unwaived High advisory → blocking (filter returns it)
+ *  2. Waived High advisory (GHSA in allowlist) → not blocking
+ *  3. Only moderate/low advisories → not blocking (advisory-only)
+ *  4. No advisories → not blocking
+ */
+
+import assert from 'node:assert/strict';
+import { test } from 'node:test';
+import { selectBlocking, partitionAdvisories } from '../check-audit.mjs';
+
+// Fixture: a High advisory not in the allowlist
+const highUnwaived = {
+  '1': {
+    severity: 'high',
+    github_advisory_id: 'GHSA-test-unwaived-high',
+    module_name: 'some-package',
+    title: 'Some high vulnerability',
+  },
+};
+
+// Fixture: a High advisory that IS in the allowlist
+const highWaived = {
+  '2': {
+    severity: 'high',
+    github_advisory_id: 'GHSA-gv7w-rqvm-qjhr',
+    module_name: 'esbuild',
+    title: 'esbuild integrity-check advisory',
+  },
+};
+
+// Fixture: only moderate/low advisories
+const moderateLow = {
+  '3': {
+    severity: 'moderate',
+    github_advisory_id: 'GHSA-mod-erate-test',
+    module_name: 'another-package',
+    title: 'Moderate vulnerability',
+  },
+  '4': {
+    severity: 'low',
+    github_advisory_id: 'GHSA-low-test-only',
+    module_name: 'yet-another',
+    title: 'Low vulnerability',
+  },
+};
+
+// Fixture: allowlist with the esbuild waiver
+const allowlist = {
+  'GHSA-gv7w-rqvm-qjhr': {
+    reason: 'esbuild dev transitive — not in production runtime',
+    reviewer: 'luc',
+    expires: '2026-09-01',
+  },
+};
+
+const emptyAllowlist = {};
+
+test('unwaived High advisory is blocking', () => {
+  const blocking = selectBlocking(highUnwaived, emptyAllowlist);
+  assert.equal(blocking.length, 1);
+  assert.equal(blocking[0].github_advisory_id, 'GHSA-test-unwaived-high');
+});
+
+test('waived High advisory is NOT blocking', () => {
+  const blocking = selectBlocking(highWaived, allowlist);
+  assert.equal(blocking.length, 0);
+});
+
+test('only moderate/low advisories → not blocking', () => {
+  const blocking = selectBlocking(moderateLow, emptyAllowlist);
+  assert.equal(blocking.length, 0);
+});
+
+test('no advisories → not blocking', () => {
+  const blocking = selectBlocking({}, emptyAllowlist);
+  assert.equal(blocking.length, 0);
+});
+
+test('partitionAdvisories splits blocking and advisory correctly', () => {
+  const mixed = { ...highUnwaived, ...moderateLow };
+  const { blocking, advisory } = partitionAdvisories(mixed, emptyAllowlist);
+  assert.equal(blocking.length, 1);
+  assert.equal(advisory.length, 2);
+});