Using Modernizr in Angular unit test

I have an Angular app defined within a Grails gsp. The Modernizr library is included at the gsp level.

I need to use the library within a directive unit test. Since I don't have Modernizr defined as a module since it's used outside of the Angular app as well as inside it, how do I inject it into my Angular unit test?

Here's my directive:

'use strict';

angular.module('simplify.directives').directive('img', ['$timeout', function ($timeout) {
    return {
        restrict: 'A',
        link: function (elem, attrs) {
            if ( typeof Modernizr !== 'undefined' && !Modernizr.svg ) {
                $timeout(function(){
                    elem.attr('src', attrs.src.replace('.svg', '.png'));
                });
            }
        }
    };
}]);

Here's my unit test code:

'use strict';

describe('Testing SVG to PNG directive', function() {
    var scope,
        elem;

    beforeEach(module('app'));

    beforeEach(module(function($provide) {
        $provide.service('appConstants', function(){});
    }));

    beforeEach(inject(function($compile, $rootScope) {
        elem = angular.element('<img ng-src="test-img.svg" />');
        scope = $rootScope;
        $compile(elem)(scope);
        scope.$digest();
    }));

    it('Should swap svg for png image if svg is not supported', function() {
       //force Modernizr.svg to be undefined here for purposes of the test
        expect(elem.attr('src')).toBe('test-img.png');
    });

});

What's the best-practice way to do this?