chore: add GitHub Actions workflow for Node.js tests

Author: Yukaii

.github/workflows/test.yml

@@ -0,0 +1,31 @@
+name: Node.js Tests
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+    
+    - name: Set up Node.js
+      uses: actions/setup-node@v4
+      with:
+        node-version: '20'
+        cache: 'npm'
+        cache-dependency-path: nodejs/package-lock.json
+
+    - name: Install dependencies
+      working-directory: nodejs
+      run: npm ci
+
+    - name: Run tests
+      working-directory: nodejs
+      env:
+        HACKMD_ACCESS_TOKEN: "test_token_123456789"
+      run: npm test