AngularJs Unit Testing isolated scope Directive

I want to test the following directive "spinInput" which requires ngModel, but I can't access the directive's scope. All I get is an empty scope. Angularjs 1.3.13 is used.

Directive:

angular.module('charts.spinInput',[]).directive('spinInput', function() {
return {
    restrict: 'E',
    replace: true,
    require:'ngModel',
    scope: {
      min:"@"
    },
    controller:function($scope)
    {
        $scope.test=12;

      $scope.calcAngle=function(point)
        {
            var xDif=point.x-50;
            var yDif=point.y-50;

            return (Math.atan2(yDif, xDif) * 180 / Math.PI);

        };

},

    templateUrl: 'charts/directive/spinInput/spinInput.html',
    link:function(scope, element, attr,ngModel) {
       ...
    }

    };
});

Unit Test: throws following error: TypeError: 'undefined' is not an object (evaluating 'innerScope.min')

 describe('spinInput', function() {

 beforeEach(module('charts'));

    var $httpBackend;
    var element;
    var outerScope;
    var innerScope;




    beforeEach(inject(function($rootScope, $compile  , $injector) {
        element = angular.element('<spin-input min="12"></spin-input>');
        $httpBackend = $injector.get('$httpBackend');
        $httpBackend.whenGET('charts/directive/spinInput/spinInput.html').respond(200, '');
        outerScope = $rootScope.$new();
        $compile(element)(outerScope);

        innerScope = element.isolateScope();

        outerScope.$digest();
    }));


    it('scope.min should be defined', function() {
        expect(innerScope.min).toBeDefined();
    });


});