When you run all of the tests (depending on order), the actual exports run (therefore `Ember.isEmpty` does exist).  When you run only this packages tests using local `rackup` with a url of http://localhost:9292/?package=ember-handlebars you would have gotten this error also.

`rake test` runs a number of different sets of QUnit URL params.  Here is a list (possibly not complete):

* Each packages tests.
* Each packages tests with optional features enabled.
* The final built output against all tests (actual confirming that the generated `dist/ember.js` file is usable).
* The final built + minified output against all tests (to ensure that the minification does not break the tests).