diff --git a/app/test/releases.test.js b/app/test/releases.test.js
index 3f24e04..e9a7c2c 100644
--- a/app/test/releases.test.js
+++ b/app/test/releases.test.js
@@ -3,7 +3,7 @@
 const test = require('node:test');
 const assert = require('node:assert/strict');
 
-const { fetchReleases } = require('../releases');
+const { fetchReleases, truncateString } = require('../releases');
 
 // 以可控的假回應替換全域 fetch，並於結束後還原
 function withFetch(handler, run) {
@@ -77,6 +77,15 @@ test('fetchReleases 對無法解析的 JSON 回應拋錯', async () => {
     );
 });
 
+test('truncateString 以字元截斷且不拆分多位元組字元（emoji 代理對）', () => {
+    const emojis = '😀'.repeat(25);
+    const result = truncateString(emojis, 10);
+    // 應得到完整 10 個 emoji（以 code point 計），不殘留落單的代理碼元
+    assert.equal(Array.from(result).length, 10);
+    assert.equal(result, '😀'.repeat(10));
+    assert.ok(!/[\uD800-\uDBFF](?![\uDC00-\uDFFF])/.test(result), '不應殘留落單的高代理碼元');
+});
+
 test('fetchReleases 解析失敗時截斷過長的回應片段', async () => {
     const huge = `{${'x'.repeat(5000)}`;
     await withFetch(