fix unit tests

src/routes/system.routes.test.ts

@@ -30,17 +30,15 @@ vi.mock('util', async (importOriginal) => {
   };
 });
 
-// FIX: Use the simple factory pattern for child_process to avoid default export issues
-vi.mock('child_process', () => {
-  const mockExec = vi.fn((command, callback) => {
-    if (typeof callback === 'function') {
-      callback(null, 'PM2 OK', '');
-    }
-    return { unref: () => {} };
-  });
-
+// The `importOriginal` pattern is the robust way to mock built-in Node modules.
+// It preserves the module's original structure, preventing "No default export" errors
+// that can occur with simple factory mocks when using ESM-based test runners like Vitest.
+vi.mock('child_process', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('child_process')>();
   return {
-    exec: mockExec,
+    ...actual,
+    // We provide a basic mock function that will be implemented in each test.
+    exec: vi.fn(),
   };
 });