title: JEST: how to test function which is executed before any render occurs in React app
body: <p>I have very short experience with JEST testing. In my React App I have (main)index file with such the content:</p>
  <pre><code>import ReactDOM from 'react-dom';
  import App from './App';
  import AppProvider from './components/AppProvider';
  import breakWhenInternetExplorer from './js/breakWhenInternetExplorer';
  
  breakWhenInternetExplorer();
  
  ReactDOM.render(
      &lt;AppProvider&gt;
          &lt;App /&gt;
      &lt;/AppProvider&gt;,
  
      document.getElementById('root'),
  );
  </code></pre>
  <p>and I'd like to test breakWhenInternetExplorer function call. While testing real components is well documented, I have no clue how to test this function call which has palce before anything else happens. Any ideas?</p>