title: How to inject external JS from CDN to Jest unit testing?
body: <p>I have react application with npm and webpack.  I'm trying to add unit testing to it.</p>
  
  <p>I'm using jQuery from CDN included in my index.html rather than using node module.</p>
  
  <p>I'm using jQuery in a Component <code>Test1</code> to which I added Unit test cases.</p>
  
  <p>Now, when I'm executing test cases I'm getting error saying
  <code>
  ReferenceError: $ is not defined
  </code>
  I understand that Jest is not able to resolve it as I didn't import jQuery import in Component.</p>
  
  <p>Question is, How to let Jest know about external JS?</p>