App.test.js

import CommentBox from "../CommentBox";
it("shows a comment box ", () => {
  // make a div
  const div = document.createElement("div");

  // shows the div we created
  ReactDOM.render(<App />, div);

  // Looks inside the div
  // and check to see if the CommentBox is in there
  // console.log(div.innerHTML);

  // bad practice
  // expect(div.innerHTML).toContain('Comment Box')

  // clean up code
  ReactDOM.unmountComponentAtNode(div);
});