Karma - Expected undefined to equal

I've got my mock window object and method:

var window = {
    open: function (url, target, specs) {
        var spec, specKey;
        this.href = url;
        this.target = target;
        // Parse through the spec string to grab the parameters you passed through
        var specArray = specs.split(',');
        for (specKey in specArray) {
            spec = specArray[specKey].split('=');
            this[String.trim(spec[0])] = String.trim(spec[1]);
        }
    }
};

and my test case:

describe('$scope.popup1', function () {

    it('should open a popup window when ISIN hyperlink is clicked within grid, passing ISIN object s values to shareDataService', inject(function ($window) {
        spyOn($window, 'open').and.callFake(function () {
            return true;
        });
        scope.popup1()
        expect(window.open).toHaveBeenCalled();
        expect(window.open.href).toEqual("views/Box_Ladder.html");
    })
   )
})

But I get Expected undefined to equal 'views/Box_Ladder.html'. I'm not sure how window.open.href is undefined seeing as I declared it above?