get rid of mockImplementation(() => promise) - causing memory leaks

src/pages/admin/components/AdminBrandManager.test.tsx

@@ -1,6 +1,6 @@
 // src/pages/admin/components/AdminBrandManager.test.tsx
 import React from 'react';
-import { render, screen, fireEvent, waitFor } from '@testing-library/react';
+import { render, screen, fireEvent, waitFor, act } from '@testing-library/react';
 import { describe, it, expect, vi, beforeEach } from 'vitest';
 import toast from 'react-hot-toast';
 import { AdminBrandManager } from './AdminBrandManager';
@@ -24,10 +24,18 @@ describe('AdminBrandManager', () => {
     vi.clearAllMocks();
   });
 
-  it('should render a loading state initially', () => {
-    mockedApiClient.fetchAllBrands.mockReturnValue(new Promise(() => {})); // Never resolves
+  it('should render a loading state initially', async () => {
+    let resolvePromise: (value: Response) => void;
+    const mockPromise = new Promise<Response>(resolve => {
+      resolvePromise = resolve;
+    });
+    mockedApiClient.fetchAllBrands.mockReturnValue(mockPromise);
     render(<AdminBrandManager />);
     expect(screen.getByText('Loading brands...')).toBeInTheDocument();
+    await act(async () => {
+      resolvePromise(new Response(JSON.stringify([])));
+      await mockPromise;
+    });
   });
 
   it('should render an error message if fetching brands fails', async () => {