set up react testing library

Author: udaypydi

src/__tests__/app.spec.js

@@ -0,0 +1,9 @@
+import { render } from '@testing-library/react';
+import '@testing-library/jest-dom/extend-expect';
+import App from '../app.jsx';
+
+it('should take a snapshot', () => {
+    const { asFragment } = render(<App />)
+    
+    expect(asFragment(<App />)).toMatchSnapshot()
+});