packages/app: add simple test

frontend/packages/app/src/App.test.tsx

@@ -0,0 +1,10 @@
+import React from 'react';
+import { render } from '@testing-library/react';
+import App from './App';
+
+describe('App', () => {
+  it('should render', () => {
+    const rendered = render(<App />);
+    expect(rendered.baseElement).toBeInTheDocument();
+  });
+});