How can I do this in Mocha?

gistfile1.js

/** @jsx React.DOM */

var React = require('react');
var Loader = require('../../lib/react-loader');
var expect = require('chai').expect;

var loader, loaded;

describe('Loader', function () {
  beforeEach(function () {
    loader = <Loader loaded={loaded}>Welcome</Loader>;
    React.renderComponent(loader, document.body);
  });

  describe('before loaded', function () {
    beforeEach(function () {
      loaded = false;
    });

    it('renders the loader', function () {
      expect(document.body.innerHTML).to.match(/<div class="loader"/);
    });

    it('does not render the content', function () {
      expect(document.body.innerHTML).to.not.match(/Welcome/);
    });
  });

  describe('after loaded', function () {
    beforeEach(function () {
      loaded = true;
    });

    it('does not render the loader', function () {
      expect(document.body.innerHTML).to.not.match(/<div class="loader"/);
    });

    it('renders the content', function () {
      expect(document.body.innerHTML).to.match(/Welcome/);
    });
  });
});

Long live rspec :)