test: add unit tests with vitest

- Add vitest configuration
- Add tests for types (Zod schemas validation)
- Add tests for inputs (parsing and validation)
- Add tests for utils (lock file detection)
- Update CI workflow to run unit tests

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: fengmk2

.github/workflows/test.yml

@@ -77,6 +77,9 @@ jobs:
       - name: Type check
         run: pnpm run typecheck
 
+      - name: Unit tests
+        run: pnpm test
+
       - name: Build
         run: pnpm run build
 

package.json

@@ -6,7 +6,9 @@
   "packageManager": "pnpm@10.28.0",
   "scripts": {
     "build": "tsdown",
-    "typecheck": "tsc --noEmit"
+    "typecheck": "tsc --noEmit",
+    "test": "vitest run",
+    "test:watch": "vitest"
   },
   "dependencies": {
     "@actions/cache": "^4.0.0",
@@ -19,6 +21,7 @@
   "devDependencies": {
     "@types/node": "^22.0.0",
     "tsdown": "latest",
-    "typescript": "^5.7.0"
+    "typescript": "^5.7.0",
+    "vitest": "^4.0.17"
   }
 }