Ember QUnit test is failing. Don't know why

I’m updating my unit tests to use the new Ember-QUnit approach and I’m running into a problem with one computed property test.

I’m trying to test that hire_date returns the correct string, but the test keeps failing with undefined is not a function. I know the setup is correct because another test, location_class, works just fine.

Can anyone offer insight as to why this is failing?

Source: 	
TypeError: undefined is not a function
    at null.<anonymous> (http://0.0.0.0:8844/app/js/application.js:146:29)
    at ComputedPropertyPrototype.get (http://0.0.0.0:8844/test/packages/ember/ember.js:4951:38)
    at get (http://0.0.0.0:8844/test/packages/ember/ember.js:2176:17)
    at Ember.Observable.Ember.Mixin.create.get (http://0.0.0.0:8844/test/packages/ember/ember.js:12425:12)
    at Object.<anonymous> (http://0.0.0.0:8844/test/model-person-test-qunit.js:26:21)
    at Object.wrapper (http://0.0.0.0:8844/test/packages/ember-qunit/dist/globals/main.js:243:27)
    at Object.Test.run (http://0.0.0.0:8844/test/packages/qunit/qunit/qunit.js:1303:18)
    at http://0.0.0.0:8844/test/packages/qunit/qunit/qunit.js:1463:10
    at process (http://0.0.0.0:8844/test/packages/qunit/qunit/qunit.js:1016:24)
    at http://0.0.0.0:8844/test/packages/qunit/qunit/qunit.js:186:5

Here’s a gist containing pertinent pieces of my code.

https://gist.github.com/commadelimited/11260080