preprocessor-v1.js

var ReactTools = require('react-tools');
var babel = require('babel-jest').process;
module.exports = {
  process: function(src, filename) {
    if (!filename.match(/\.jsx$/)) {
      return '';
    }
    return ReactTools.transform(babel(src, filename));
  }
};

/**
 * - TypeError: app\scripts\components\TestComponent.jsx: undefined is not a function
        at app\scripts\components\TestComponent.jsx:4:27
        at Suite.<anonymous> (app\scripts\components\__tests__\TestComponent-test.jsx:6:23)
        at env.describe_ (<anonymous>:40:25)
        at env.describe (<anonymous>:27:19)
        at describe (node_modules\jest-cli\vendor\jasmine\jasmine-1.3.0.js:604:27)
        at app\scripts\components\__tests__\TestComponent-test.jsx:4:1
        */

preprocessor-v2.js

var babel = require('babel');

module.exports = {
  process: function(src, filename) {
    // Ignore files other than .js, .es, .jsx or .es6
    if (!babel.canCompile(filename)) {
      return '';
    }
    // Ignore all files within node_modules
    if (filename.indexOf('node_modules') === -1) {
      return babel.transform(src, {filename: filename}).code;
    }
    return src;
  }
};

/**
 * Error: Worker process exited before responding! exit code: 3221225477, exit signal: null
stderr:


A worker process has quit unexpectedly! This is bad news, shutting down now!
npm ERR! Test failed.  See above for more details.
*/

TestComponent-test.jsx

jest.dontMock('../TestComponent');
describe('test component', function() {
  var TestComponent = require('../TestComponent');
});

TestComponent.jsx

var React = require('react');
var TestComponent = React.createClass({
  render () {
    return (
      <div>
        Hello, test!
      </div>
    );
  }
});
module.exports = TestComponent;