diff --git a/app/index.test.js b/app/index.test.js
new file mode 100644
index 0000000..e609483
--- /dev/null
+++ b/app/index.test.js
@@ -0,0 +1,79 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  truncateDiff,
+  fallbackSummary,
+  buildResolveBranchName,
+  buildResolveBody,
+} from './index.js';
+
+test('truncateDiff: 內容在上限內不截斷', () => {
+  const { diff, truncated } = truncateDiff('abc', 100);
+  assert.equal(diff, 'abc');
+  assert.equal(truncated, false);
+});
+
+test('truncateDiff: null/空字串回傳空字串且不截斷', () => {
+  assert.deepEqual(truncateDiff(null, 100), { diff: '', truncated: false });
+  assert.deepEqual(truncateDiff('', 100), { diff: '', truncated: false });
+});
+
+test('truncateDiff: 超過上限時截斷並標示', () => {
+  const big = 'x'.repeat(50);
+  const { diff, truncated } = truncateDiff(big, 10);
+  assert.equal(truncated, true);
+  assert.ok(diff.startsWith('xxxxxxxxxx'));
+  assert.ok(diff.includes('已截斷'));
+});
+
+test('fallbackSummary: 取首個 commit 當標題', () => {
+  const s = fallbackSummary({
+    source: 'feature',
+    target: 'develop',
+    commitMessages: '- feat: 新增功能\n- fix: 修正',
+    diffStat: ' a.js | 2 +-',
+  });
+  assert.equal(s.title, 'feat: 新增功能');
+  assert.ok(s.description.includes('## 變更摘要'));
+  assert.ok(s.description.includes('a.js'));
+});
+
+test('fallbackSummary: 無 commit 時退回 Merge 標題且描述非空', () => {
+  const s = fallbackSummary({
+    source: 'feature',
+    target: 'develop',
+    commitMessages: '',
+    diffStat: '',
+  });
+  assert.equal(s.title, 'Merge feature into develop');
+  assert.ok(s.description.includes('(無)'));
+  assert.ok(s.description.length > 0);
+});
+
+test('buildResolveBranchName: 含前綴並淨化非法字元', () => {
+  const name = buildResolveBranchName('develop', 'feature/x y');
+  assert.ok(name.startsWith('resolve-conflict/'));
+  assert.ok(name.includes('-into-'));
+  // 空白等非法字元被替換為 -
+  assert.ok(!/\s/.test(name));
+});
+
+test('buildResolveBranchName: 過長 target/source 仍遠低於 255', () => {
+  const long = 'a'.repeat(500);
+  const name = buildResolveBranchName(long, long);
+  assert.ok(name.length < 255);
+});
+
+test('buildResolveBody: 含衝突檔案清單與人工檢查清單', () => {
+  const body = buildResolveBody({
+    source: 'feature',
+    target: 'develop',
+    resolveBranch: 'resolve-conflict/develop-into-feature',
+    files: ['a.js', 'b.js'],
+    summary: { title: 't', description: '摘要內容' },
+  });
+  assert.ok(body.includes('- `a.js`'));
+  assert.ok(body.includes('- `b.js`'));
+  assert.ok(body.includes('合併前人工檢查清單'));
+  assert.ok(body.includes('摘要內容'));
+});
diff --git a/app/lib/git.test.js b/app/lib/git.test.js
new file mode 100644
index 0000000..4b5e127
--- /dev/null
+++ b/app/lib/git.test.js
@@ -0,0 +1,114 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { mkdtempSync, writeFileSync, rmSync, readFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { execFileSync } from 'node:child_process';
+import { Git } from './git.js';
+
+function g(cwd, args) {
+  return execFileSync('git', args, { cwd, encoding: 'utf8' });
+}
+
+/** 建立 bare remote + working clone，於 target/source 製造會衝突的變更。 */
+function setupRepo() {
+  const root = mkdtempSync(join(tmpdir(), 'git-test-'));
+  const bare = join(root, 'remote.git');
+  const work = join(root, 'work');
+  execFileSync('git', ['init', '-q', '--bare', bare]);
+  execFileSync('git', ['clone', '-q', bare, work]);
+  g(work, ['config', 'user.email', 'test@example.com']);
+  g(work, ['config', 'user.name', 'tester']);
+  g(work, ['config', 'commit.gpgsign', 'false']);
+
+  writeFileSync(join(work, 'file.txt'), 'base\n');
+  g(work, ['add', '-A']);
+  g(work, ['commit', '-q', '-m', 'base']);
+  const def = g(work, ['rev-parse', '--abbrev-ref', 'HEAD']).trim();
+
+  g(work, ['checkout', '-q', '-b', 'target']);
+  writeFileSync(join(work, 'file.txt'), 'target change\n');
+  g(work, ['commit', '-qam', 'target change']);
+
+  g(work, ['checkout', '-q', def]);
+  g(work, ['checkout', '-q', '-b', 'source']);
+  writeFileSync(join(work, 'file.txt'), 'source change\n');
+  g(work, ['commit', '-qam', 'source change']);
+
+  g(work, ['push', '-q', 'origin', 'target', 'source', def]);
+  return { root, bare, work };
+}
+
+test('detectConflict: 偵測到衝突並回傳衝突檔，事後還原暫存分支', () => {
+  const { root, bare, work } = setupRepo();
+  try {
+    const git = new Git({ cwd: work, remoteUrl: bare, token: 'x' });
+    git.configure();
+    git.fetchBranches(['target', 'source']);
+
+    assert.ok(git.countAheadCommits('target', 'source') >= 1);
+
+    const det = git.detectConflict('target', 'source');
+    assert.equal(det.hasConflict, true);
+    assert.ok(det.files.includes('file.txt'));
+
+    // 暫存分支應已清除
+    assert.ok(!g(work, ['branch']).includes('__conflict_check'));
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});
+
+test('createResolveBranch: 推送含衝突標記的解衝突分支到 remote', () => {
+  const { root, bare, work } = setupRepo();
+  try {
+    const git = new Git({ cwd: work, remoteUrl: bare, token: 'x' });
+    git.configure();
+    git.fetchBranches(['target', 'source']);
+
+    const res = git.createResolveBranch({ target: 'target', source: 'source', resolveBranch: 'resolve-x' });
+    assert.ok(res.files.includes('file.txt'));
+
+    // remote 應有 resolve-x 分支
+    assert.ok(execFileSync('git', ['--git-dir', bare, 'branch'], { encoding: 'utf8' }).includes('resolve-x'));
+    // 已 commit 的檔案應保留衝突標記
+    assert.ok(readFileSync(join(work, 'file.txt'), 'utf8').includes('<<<<<<<'));
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});
+
+test('detectConflict: 可順利合併時回報無衝突', () => {
+  const root = mkdtempSync(join(tmpdir(), 'git-test-'));
+  try {
+    const bare = join(root, 'remote.git');
+    const work = join(root, 'work');
+    execFileSync('git', ['init', '-q', '--bare', bare]);
+    execFileSync('git', ['clone', '-q', bare, work]);
+    g(work, ['config', 'user.email', 'test@example.com']);
+    g(work, ['config', 'user.name', 'tester']);
+    g(work, ['config', 'commit.gpgsign', 'false']);
+
+    writeFileSync(join(work, 'a.txt'), 'base\n');
+    g(work, ['add', '-A']);
+    g(work, ['commit', '-qm', 'base']);
+    const def = g(work, ['rev-parse', '--abbrev-ref', 'HEAD']).trim();
+
+    g(work, ['checkout', '-q', '-b', 'target']); // target 不動
+    g(work, ['checkout', '-q', def]);
+    g(work, ['checkout', '-q', '-b', 'source']);
+    writeFileSync(join(work, 'b.txt'), 'new file\n'); // 改不同檔，無衝突
+    g(work, ['add', '-A']);
+    g(work, ['commit', '-qm', 'add b']);
+    g(work, ['push', '-q', 'origin', 'target', 'source', def]);
+
+    const git = new Git({ cwd: work, remoteUrl: bare, token: 'x' });
+    git.configure();
+    git.fetchBranches(['target', 'source']);
+    const det = git.detectConflict('target', 'source');
+    assert.equal(det.hasConflict, false);
+    assert.deepEqual(det.files, []);
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});
diff --git a/app/lib/gitea.test.js b/app/lib/gitea.test.js
new file mode 100644
index 0000000..9823e76
--- /dev/null
+++ b/app/lib/gitea.test.js
@@ -0,0 +1,78 @@
+import { test, afterEach } from 'node:test';
+import assert from 'node:assert/strict';
+import { GiteaClient } from './gitea.js';
+
+const realFetch = globalThis.fetch;
+afterEach(() => { globalThis.fetch = realFetch; });
+
+function makeClient() {
+  return new GiteaClient({
+    serverUrl: 'https://gitea.example',
+    owner: 'o',
+    repo: 'r',
+    token: 't',
+  });
+}
+
+/** 建立假的 fetch，依序回傳給定的回應。 */
+function stubFetch(responses) {
+  const calls = [];
+  globalThis.fetch = async (url, opts) => {
+    calls.push({ url, opts });
+    const r = responses.shift();
+    return {
+      ok: r.status >= 200 && r.status < 300,
+      status: r.status,
+      text: async () => (r.body == null ? '' : JSON.stringify(r.body)),
+    };
+  };
+  return calls;
+}
+
+test('createPull: 成功建立回傳 created=true', async () => {
+  stubFetch([{ status: 201, body: { number: 7, html_url: 'u' } }]);
+  const { pull, created } = await makeClient().createPull({
+    head: 'feature', base: 'develop', title: 't', body: 'b',
+  });
+  assert.equal(created, true);
+  assert.equal(pull.number, 7);
+});
+
+test('createPull: 422 已存在時回查既有 PR，created=false', async () => {
+  stubFetch([
+    { status: 422, body: { message: 'already exists' } },
+    { status: 200, body: [
+      { number: 3, head: { ref: 'feature' }, base: { ref: 'develop' } },
+    ] },
+  ]);
+  const { pull, created } = await makeClient().createPull({
+    head: 'feature', base: 'develop', title: 't', body: 'b',
+  });
+  assert.equal(created, false);
+  assert.equal(pull.number, 3);
+});
+
+test('createPull: 422 但查無對應 PR 時丟出錯誤', async () => {
+  stubFetch([
+    { status: 422, body: { message: 'bad' } },
+    { status: 200, body: [] },
+  ]);
+  await assert.rejects(
+    () => makeClient().createPull({ head: 'feature', base: 'develop', title: 't', body: 'b' }),
+    /建立 PR 失敗/,
+  );
+});
+
+test('createPull: 其他錯誤狀態碼直接丟出', async () => {
+  stubFetch([{ status: 500, body: { message: '伺服器錯誤' } }]);
+  await assert.rejects(
+    () => makeClient().createPull({ head: 'feature', base: 'develop', title: 't', body: 'b' }),
+    /建立 PR 失敗 \(500\)/,
+  );
+});
+
+test('findOpenPull: 非陣列回應回傳 null', async () => {
+  stubFetch([{ status: 200, body: { unexpected: true } }]);
+  const r = await makeClient().findOpenPull('feature', 'develop');
+  assert.equal(r, null);
+});
diff --git a/app/lib/opencode.test.js b/app/lib/opencode.test.js
new file mode 100644
index 0000000..7ead244
--- /dev/null
+++ b/app/lib/opencode.test.js
@@ -0,0 +1,41 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { extractResult } from './opencode.js';
+
+test('extractResult: 解析乾淨的 JSON', () => {
+  const r = extractResult('{"title":"標題","description":"描述"}');
+  assert.deepEqual(r, { title: '標題', description: '描述' });
+});
+
+test('extractResult: 忽略 JSON 前後的雜訊文字', () => {
+  const r = extractResult('以下是結果：\n{"title":"T","description":"D"}\n完成');
+  assert.deepEqual(r, { title: 'T', description: 'D' });
+});
+
+test('extractResult: 修正字串值內未跳脫的換行', () => {
+  // LLM 常輸出字串內含真實換行的無效 JSON
+  const r = extractResult('{"title":"T","description":"第一行\n第二行"}');
+  assert.equal(r.title, 'T');
+  assert.equal(r.description, '第一行\n第二行');
+});
+
+test('extractResult: 去除 ANSI 控制碼後解析', () => {
+  const r = extractResult('\x1b[32m{"title":"T","description":"D"}\x1b[0m');
+  assert.deepEqual(r, { title: 'T', description: 'D' });
+});
+
+test('extractResult: 挑出第一個含 title 的物件', () => {
+  const r = extractResult('{"foo":1}\n{"title":"對的","description":"D"}');
+  assert.equal(r.title, '對的');
+});
+
+test('extractResult: 無有效物件回傳 null', () => {
+  assert.equal(extractResult('沒有任何 JSON'), null);
+  assert.equal(extractResult(''), null);
+  assert.equal(extractResult('{"description":"缺少 title"}'), null);
+});
+
+test('extractResult: description 缺漏時以空字串補上', () => {
+  const r = extractResult('{"title":"只有標題"}');
+  assert.deepEqual(r, { title: '只有標題', description: '' });
+});
diff --git a/app/lib/util.test.js b/app/lib/util.test.js
new file mode 100644
index 0000000..13d2bc2
--- /dev/null
+++ b/app/lib/util.test.js
@@ -0,0 +1,37 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { maskSecrets, run } from './util.js';
+
+test('maskSecrets: 遮蔽出現的祕密字串', () => {
+  const out = maskSecrets('token is abcd1234 here', ['abcd1234']);
+  assert.equal(out, 'token is *** here');
+});
+
+test('maskSecrets: 遮蔽 URL 內嵌的 token', () => {
+  const out = maskSecrets('https://oauth2:abcd1234@host/repo.git', ['abcd1234']);
+  assert.ok(!out.includes('abcd1234'));
+});
+
+test('maskSecrets: 太短(<4)的祕密不遮蔽以免誤傷', () => {
+  assert.equal(maskSecrets('abc here', ['abc']), 'abc here');
+});
+
+test('maskSecrets: 多個祕密與空值都安全處理', () => {
+  const out = maskSecrets('aaaa bbbb', ['aaaa', '', undefined, 'bbbb']);
+  assert.equal(out, '*** ***');
+});
+
+test('maskSecrets: 非字串輸入回傳空字串', () => {
+  assert.equal(maskSecrets(null), '');
+});
+
+test('run: 非零結束碼不丟例外並回傳 status', () => {
+  const r = run('node', ['-e', 'process.exit(3)']);
+  assert.equal(r.status, 3);
+});
+
+test('run: 指令不存在時回傳 status=1 與錯誤訊息', () => {
+  const r = run('a-command-that-does-not-exist-xyz', []);
+  assert.equal(r.status, 1);
+  assert.ok(r.stderr.length > 0);
+});
diff --git a/app/package.json b/app/package.json
index 136121a..48c5e84 100644
--- a/app/package.json
+++ b/app/package.json
@@ -5,7 +5,8 @@
   "type": "module",
   "main": "index.js",
   "scripts": {
-    "start": "node index.js"
+    "start": "node index.js",
+    "test": "node --test"
   },
   "engines": {
     "node": ">=18"