diff --git a/app/test/delete-utils.test.js b/app/test/delete-utils.test.js
new file mode 100644
index 0000000..e2814cd
--- /dev/null
+++ b/app/test/delete-utils.test.js
@@ -0,0 +1,97 @@
+import { test } from 'node:test'
+import assert from 'node:assert/strict'
+import {
+  isRetryableStatus,
+  deleteWithRetry,
+  runWithConcurrency,
+} from '../delete-utils.js'
+
+const noSleep = () => Promise.resolve()
+
+test('isRetryableStatus 僅對暫時性狀態碼回傳 true', () => {
+  for (const s of [429, 502, 503, 504]) assert.equal(isRetryableStatus(s), true)
+  for (const s of [200, 204, 400, 401, 403, 404, 500]) {
+    assert.equal(isRetryableStatus(s), false)
+  }
+})
+
+test('deleteWithRetry 成功(204)時不重試', async () => {
+  let calls = 0
+  const client = {
+    async deleteResource() {
+      calls += 1
+      return 204
+    },
+  }
+  const result = await deleteWithRetry(client, 'u', { sleep: noSleep })
+  assert.equal(result.status, 204)
+  assert.equal(calls, 1)
+})
+
+test('deleteWithRetry 對暫時性錯誤重試後成功', async () => {
+  const statuses = [503, 503, 204]
+  let i = 0
+  const client = {
+    async deleteResource() {
+      return statuses[i++]
+    },
+  }
+  const result = await deleteWithRetry(client, 'u', { sleep: noSleep })
+  assert.equal(result.status, 204)
+  assert.equal(result.attempts, 3)
+})
+
+test('deleteWithRetry 對永久性錯誤(403)立即停止重試', async () => {
+  let calls = 0
+  const client = {
+    async deleteResource() {
+      calls += 1
+      return 403
+    },
+  }
+  const result = await deleteWithRetry(client, 'u', { sleep: noSleep })
+  assert.equal(result.status, 403)
+  assert.equal(calls, 1)
+})
+
+test('deleteWithRetry 對網路例外重試至次數用盡並回傳 error', async () => {
+  let calls = 0
+  const client = {
+    async deleteResource() {
+      calls += 1
+      throw new Error('network down')
+    },
+  }
+  const result = await deleteWithRetry(client, 'u', { attempts: 3, sleep: noSleep })
+  assert.equal(result.status, 0)
+  assert.match(result.error.message, /network down/)
+  assert.equal(calls, 3)
+})
+
+test('runWithConcurrency 回傳對應輸入順序的結果', async () => {
+  const items = [1, 2, 3, 4, 5]
+  const out = await runWithConcurrency(items, async (n) => n * 2, 2)
+  assert.deepEqual(out, [2, 4, 6, 8, 10])
+})
+
+test('runWithConcurrency 不超過併發上限', async () => {
+  let active = 0
+  let maxActive = 0
+  const items = Array.from({ length: 10 }, (_, i) => i)
+  await runWithConcurrency(
+    items,
+    async () => {
+      active += 1
+      maxActive = Math.max(maxActive, active)
+      await Promise.resolve()
+      active -= 1
+    },
+    3,
+  )
+  assert.ok(maxActive <= 3, `maxActive=${maxActive} 應 <= 3`)
+})
+
+test('runWithConcurrency 對空陣列回傳空陣列', async () => {
+  const out = await runWithConcurrency([], async () => 1, 4)
+  assert.deepEqual(out, [])
+})