title: Babel / Karma / Chai gives TypeError: 'caller', 'callee', and 'arguments' properties may not be accessed on strict mode functions
body: <p>I having trouble figuring out why this test is not passing.</p>
  
  <pre><code>var expect = require('chai').expect;
  
  describe('HelloComponent', function() {
  
    it('passes a quite simple test', function() {
      expect(1 + 4).to.equal(5);
    });
  
  });
  </code></pre>
  
  <p>produces this error:</p>
  
  <pre><code>DEBUG [web-server]: serving: /Users/ivan/dev/react-starter/node_modules/karma/static/context.html
  DEBUG [web-server]: serving (cached): /Users/ivan/dev/react-starter/node_modules/mocha/mocha.js
  DEBUG [web-server]: serving (cached): /Users/ivan/dev/react-starter/node_modules/karma-mocha/lib/adapter.js
  DEBUG [web-server]: serving (cached): /Users/ivan/dev/react-starter/test/front-end/tests.webpack.js
  Chrome 41.0.2272 (Mac OS X 10.10.2) HelloComponent passes a quite simple test FAILED
          TypeError: 'caller', 'callee', and 'arguments' properties may not be accessed on strict mode functions or the arguments objects for calls to them
              at new Assertion (/Users/ivan/dev/react-starter/test/front-end/tests.webpack.js:2166:43 &lt;- webpack:///~/chai/lib/chai/assertion.js:33:42)
              at chai.expect (/Users/ivan/dev/react-starter/test/front-end/tests.webpack.js:3592:13 &lt;- webpack:///~/chai/lib/chai/interface/expect.js:9:11)
              at Context.&lt;anonymous&gt; (/Users/ivan/dev/react-starter/test/front-end/tests.webpack.js:89:6 &lt;- webpack:///test/front-end/hello-spec.js:10:4)
  </code></pre>
  
  <p>It might have something to do with babel wrapping things in strict mode? </p>
  
  <p>Does anyone know what steps I can start to take to figure out what's going here?</p>
  
  <p>The code is open source and available here:
  <a href="https://github.com/UWFosterIT/react-starter/tree/gulp-webpack">https://github.com/UWFosterIT/react-starter/tree/gulp-webpack</a></p>
  
  <p>to install and reproduce this error:</p>
  
  <pre><code>git clone https://github.com/UWFosterIT/react-starter.git
  npm install
  gulp test:karma
  </code></pre>