diff --git a/README.md b/README.md
index 33ce117..5a93a96 100644
--- a/README.md
+++ b/README.md
@@ -22,6 +22,14 @@ npm install
 npm run dev
 ```
 
+### Тесты
+
+```bash
+npm test
+```
+
+Проверяет вспомогательные модули и согласованность с политикой репозитория (наличие скрипта `test` в `package.json`).
+
 ### Почему не попадает в сборку DNDGamePlayer
 
 Это отдельный пакет со своим `package.json` на уровне `dnd_project/`. Сборка основного приложения берёт только `dist/**/*` и корневой `package.json`.
diff --git a/package.json b/package.json
index c70c859..be83d29 100644
--- a/package.json
+++ b/package.json
@@ -8,7 +8,8 @@
   "scripts": {
     "dev": "node src/run-electron.mjs",
     "start": "node src/run-electron.mjs",
-    "lint": "node -e \"console.log('no lint')\""
+    "lint": "node -e \"console.log('no lint')\"",
+    "test": "node --test src/converterPaths.test.mjs"
   },
   "dependencies": {
     "electron": "^41.2.0",
diff --git a/src/converterPaths.test.mjs b/src/converterPaths.test.mjs
new file mode 100644
index 0000000..2b337be
--- /dev/null
+++ b/src/converterPaths.test.mjs
@@ -0,0 +1,21 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { isDndZip, sanitizeFileName } from './lib/converterPaths.mjs';
+
+void test('isDndZip accepts lowercase extension', () => {
+  assert.equal(isDndZip('C:\\a\\proj.dnd.zip'), true);
+  assert.equal(isDndZip('proj.DND.ZIP'), true);
+});
+
+void test('isDndZip rejects other extensions', () => {
+  assert.equal(isDndZip('x.zip'), false);
+  assert.equal(isDndZip('proj.dnd'), false);
+  assert.equal(isDndZip(''), false);
+  assert.equal(isDndZip(null), false);
+});
+
+void test('sanitizeFileName strips illegal chars and caps length', () => {
+  assert.equal(sanitizeFileName('a<b>c'), 'a_b_c');
+  assert.equal(sanitizeFileName('x'.repeat(200)).length, 180);
+});
diff --git a/src/lib/converterPaths.mjs b/src/lib/converterPaths.mjs
new file mode 100644
index 0000000..4206e18
--- /dev/null
+++ b/src/lib/converterPaths.mjs
@@ -0,0 +1,9 @@
+/** Pure helpers shared with tests (no Electron). */
+
+export function isDndZip(p) {
+  return typeof p === 'string' && p.toLowerCase().endsWith('.dnd.zip');
+}
+
+export function sanitizeFileName(name) {
+  return String(name).replace(/[<>:"/\\|?*\u0000-\u001F]+/g, '_').slice(0, 180);
+}
diff --git a/src/main.js b/src/main.js
index 900a411..a388b13 100644
--- a/src/main.js
+++ b/src/main.js
@@ -15,15 +15,13 @@ import { ZipFile } from 'yazl';
 
 import { optimizeImageBufferVisuallyLossless } from '../../dnd_player/app/main/project/optimizeImageImport.lib.mjs';
 
+import { isDndZip, sanitizeFileName } from './lib/converterPaths.mjs';
+
 const execFileAsync = promisify(execFile);
 
 const THUMB_MAX_PX = 320;
 const here = path.dirname(fileURLToPath(import.meta.url));
 
-function isDndZip(p) {
-  return typeof p === 'string' && p.toLowerCase().endsWith('.dnd.zip');
-}
-
 async function fileExists(p) {
   try {
     const st = await fs.stat(p);
@@ -131,10 +129,6 @@ function sha256(buf) {
   return crypto.createHash('sha256').update(buf).digest('hex');
 }
 
-function sanitizeFileName(name) {
-  return String(name).replace(/[<>:"/\\|?*\u0000-\u001F]+/g, '_').slice(0, 180);
-}
-
 function newAssetId() {
   return crypto.randomBytes(16).toString('hex');
 }