Investigate using mocha.throwError

``` js
/**
 * Function to allow assertion libraries to throw errors directly into mocha.
 * This is useful when running tests in a browser because window.onerror will
 * only receive the 'message' attribute of the Error.
 */
mocha.throwError = function(err) {
  Mocha.utils.forEach(uncaughtExceptionHandlers, function (fn) {
    fn(err);
  });
  throw err;
};
```
