Add demo test script

Author: taneliang

src/context/__tests__/demo-test.js

@@ -0,0 +1,11 @@
+'use strict';
+
+import React from 'react';
+import { render, screen } from '@testing-library/react';
+import ContextMenuItem from '../ContextMenuItem';
+
+test('renders learn react link', () => {
+  render(<ContextMenuItem />);
+  const linkElement = screen.getByText(/learn react/i);
+  expect(linkElement).toBeInTheDocument();
+});