Add basic App component test

- Create App.test.js with initial React testing setup
- Verify basic rendering of learn react link
- Use React Testing Library for component testing

Author: pstackebrandt

src/App.test.js src/routes/App.test.jssrc/App.test.js renamed to src/routes/App.test.js

@@ -1,4 +1,5 @@
 import { render, screen } from '@testing-library/react';
+
 import App from './App';
 
 test('renders learn react link', () => {