Unit testing directive that modifies properties under element.sheet

So I've inherited this project at work and I'm attempting to get our unit tests up to par. I'm having issues testing this directive. It runs fine except for when unit testing. It seems that $elm.sheet is NULL when testing. What are my options here?

Update: I've attempted to assign my own object to $element.sheet so that I can monitor for changes, however, it seems that the object is frozen and immutable.

directive

var themeStyler = function(SelectedService) {
    return {
        restrict: 'E',
        template: '<style> .organization-color {} .bg-organization-color {} </style>',
        replace: true,
        scope: {},
        link: function(scope, $elm) {
            scope.organization = SelectedService.user.$organization;

            scope.$watch('organization.textColor', function(color) {
                $elm.sheet.cssRules[0].style.cssText = 'color: ' + color + ' !important;';
            });

            scope.$watch('organization.backgroundColor', function(color) {
                $elm.sheet.cssRules[1].style.cssText = 'background-color: ' + color + ' !important;';
            });
        }
    };
};

themeStyler.$inject = ['SelectedService'];
angular.module('vpower.directives').directive('themeStyler', themeStyler);

unit test

describe('theme-styler.directive', function() {
    'use strict';

    var scope;
    var container;

    beforeEach(function() {
        module('myapp-directives');
        module('myapp', function($provide) {
            $provide.value('SelectedService', {
                user: {
                    $organization: {
                        textColor: '#ffffff',
                        backgroundColor: '#ffffff'
                    }
                }
            });
        });

        inject(function($rootScope, $compile) {
            scope = $rootScope.$new();
            container = angular.element('<theme-styler></theme-styler>');

            $compile(container)(scope);
            scope.$digest();
        })
    });

    it('should compile directive element', function() {
        expect(container).toBeDefined();
    });
});