Create App.test.js

frontend-react/src/App.test.js

+import React from 'react';
+import { render } from '@testing-library/react';
+import App from './App';
+
+test('renders learn react link', () => {
+    const { getByText } = render(<App />);
+    const linkElement = getByText(/learn react/i);
+    expect(linkElement).toBeInTheDocument();
+});