diff --git a/app/index.js b/app/index.js
index 164709d..227b12f 100644
--- a/app/index.js
+++ b/app/index.js
@@ -1,3 +1,4 @@
+import { fileURLToPath } from 'node:url';
 import { loadInputs, logInputs } from './lib/inputs.js';
 import { Git } from './lib/git.js';
 import { GiteaClient } from './lib/gitea.js';
@@ -191,9 +192,15 @@ function reportPull(pull, created) {
   }
 }
 
-main().catch((err) => {
-  const detail = err?.stack || err?.message || String(err);
-  // 錯誤訊息／stack 可能夾帶 token，輸出到 CI 日誌前先遮蔽
-  log.error(maskSecrets(detail, [process.env.GITEA_TOKEN]));
-  process.exit(1);
-});
+// 純函式對外匯出，供測試使用（不觸發 main 流程）
+export { truncateDiff, fallbackSummary, buildResolveBranchName, buildResolveBody };
+
+// 僅在直接以 `node index.js` 執行時才跑主流程；被測試 import 時不執行
+if (process.argv[1] && fileURLToPath(import.meta.url) === process.argv[1]) {
+  main().catch((err) => {
+    const detail = err?.stack || err?.message || String(err);
+    // 錯誤訊息／stack 可能夾帶 token，輸出到 CI 日誌前先遮蔽
+    log.error(maskSecrets(detail, [process.env.GITEA_TOKEN]));
+    process.exit(1);
+  });
+}