title: Jest/React - How to use global object in unit tests?
body: <p>I use CommonJS modules with require() except React, which is global:</p>
  
  <pre><code>// I don't want require React in every module:
  // var React = require("react");
  
  var MyComponent = React.createClass({ // React is global here
  });
  </code></pre>
  
  <p>When running a unit test on MyComponent, Jest can't find React. Is there a way to tell Jest to insert a global React object? (I use npm and gulp-browserify.)</p>