Ember controller test is not using prototype extension when called

I am trying to unit test an Ember addon that has already been written but unfortunately did not get tested at the time of its creation. I would really really like not to have to modify the existing codebase to fit the tests if possible.

Controller Code

foo() {
    return this.get('store').query('stuff', query)
        .then((data) => {
            this.setProperties({
                myList: []
            });

            data.get('content').mapBy('record').forEach((item) => {
                // fails here
                this.get('myList').pushObject(item);
            });
        });
    });
}

Test Code

beforeEach() {
    let data = Ember.Object.create({
        content: Ember.A([
            { record: { } },
            { record: { } }
        ]);
    });

    this.controller = this.subject({
        store: {
            query(property, query) {
                return new Ember.RSVP.Promise(function (resolve) {
                    resolve(data);
                });
            }
        }
    });
}

test('failing test case', function (assert) {
    this.controller.foo();
}

Error:

Uncaught TypeError: _this.get(...).pushObject is not a function

I did some research and found out that Ember extends object prototypes by default so that standard arrays ( [] ) become Ember arrays. I've checked my config/environment.js as mentioned in the how-to-disable prototype extension here and it only returns and empty object {}.

Why doesn't Ember wrap the array and allow me to use pushObject like I would expect in my tests?

PS: I've noticed that there's a package to disable prototype extension aimed at addon authors, but again I do not have this package
http://ift.tt/2bh2EhK