jsdom + mocha testing of a React component, with no build step required.

jsdom-mocha-react

var React = require('React/addons'),
    assert = require('assert');

var Hello = React.createClass({
    render: function () {
        return React.DOM.p(null, 'hello');
    }
});

var jsdom = require('jsdom');

describe('A', function () {
    beforeEach(function () {
        global.document = jsdom.jsdom();
        global.window = document.parentWindow;
    });

    it('B', function () {
        React.renderComponent(Hello(), document.body);
        assert.equal(document.querySelector('p').innerHTML, 'hello');
    }); 
});