ryancyq
diff --git a/‎__tests__/setup.ts‎
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+import { vi } from 'vitest'
+
+// @actions/* v3+ packages ship as true ESM, whose module namespace objects are non-configurable
+// by spec, making vi.spyOn fail with "Cannot redefine property". Spreading the real exports
+// into a plain object gives Vitest a configurable target so spyOn works while keeping the
+// original implementations for anything not explicitly mocked in a test.
+// See: https://vitest.dev/guide/mocking/modules.html#jsdom-happy-dom-node
+vi.mock('@actions/core', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('@actions/core')>()
+  return { ...actual }
+})
+
+vi.mock('@actions/exec', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('@actions/exec')>()
+  return { ...actual }
+})