Ember addon. Acceptance test: undefined is not a constructor

I'm building an addon from an Ember app that I built and passes all the tests. When I try to use the same acceptance tests for the dummy app and I run the tests I get this error for lots of tests (only in PhantomJS. All the tests pass in Chrome). I'm using mocha and chai as test framework

Errors: 

undefined is not a constructor (evaluating 'app.testHelpers.findWithAssert(selector, context)')

undefined is not a constructor (evaluating 'path.includes('bla')')

undefined is not a constructor (evaluating 'currentPath()')

undefined is not a constructor (evaluating 'path.includes('bla')')