Testing Angular controllers using controllerAs - angularjs

Question

I've been slowly updating an angular app ready for a 2.0 migration when it's released and I'm running into issues updating my specs. The main problem is I've started to use the controller as syntax and remove scope from my controllers completely but now I'm having problems spying on services that are called in the context of 'this' inside the controller.
I'm copying below the controller code and the spec. I've dummed it down so we can try and solve this problem easily.
Controller:
var LoginCtrl;
LoginCtrl = (function() {
function LoginCtrl(Auth, $state, Session) {
this.Auth = Auth;
this.$state = $state;
this.Session = Session;
this.credentials = {
username: undefined,
password: undefined,
email: undefined
};
}
LoginCtrl.prototype.login = function () {
var _self = this;
this.Auth.login(this.credentials).then(function(response) {
console.log(response)
}, function(error) {
console.log(error)
});
};
return LoginCtrl;
})();
angular.module('projectx').controller('LoginCtrl', ['Auth', '$state', 'Session', LoginCtrl]);
Spec:
describe('Controller: LoginCtrl', function () {
var $controller, Auth;
beforeEach(module('projectx'));
beforeEach(inject(function(_$controller_, _Auth_) {
$controller = _$controller_;
Auth = _Auth_;
}));
it('should pass user credentials to server to log you in', function() {
var scope = {};
var login = $controller('LoginCtrl as login', {$scope: scope});
expect(scope.login).toBe(login);
spyOn(scope.login.Auth, 'login');
scope.login.credentials = {
username: 'test',
password: 'test'
};
scope.login.login();
expect(scope.login.Auth.login).toHaveBeenCalledWith({username: 'test', password: 'test'});
});
});
The error I get is 'undefined' when the controller trys to call this.Auth.login because my spec is spying on (scope.login.Auth, 'login') which is a separate instance I think? Heres the actual error:
PhantomJS 1.9.8 (Mac OS X) Controller: LoginCtrl should pass user credentials to server to log you in FAILED
TypeError: 'undefined' is not an object (evaluating 'this.Auth.login(this.credentials).then')
at /app/controllers/login.js:25
at /spec/controllers/login.js:49