JavaScript unit test: Cannot check if jQuery method was called

I have an Angular application with a very simple directive for now called animate. I am trying to check using Jasmine whether the method slideDown was called. Currently my directive looks like this:

animateDirective

var animate = function () {
    return function (scope, element, attrs) {
        scope.$watch(attrs.animate, function () {
            element.slideDown(200);
        })
    }
}

app

var app = angular.module("app", []);

app.controller("homeController", homeController);
app.directive("animate", animate);

In my unit test file I have checked that all my references are correct and I've tested in a browser and the directive is being hit. Here is my unit test class so far:

animateDirectiveUnitTests

describe("animateDirective", function () {
    var $compile;
    var $scope;
    var template = "<p animate></p>";
    var isolateScope;

    function createDirective() {
        var directiveElement = angular.element(template);
        $compile(directiveElement)($scope);
        $scope.$digest();

        return directiveElement;
    }

    beforeEach(function () {
        module("app");
        inject(function (_$compile_, _$rootScope_) {
            $compile = _$compile_;
            $scope = _$rootScope_.$new();
        });
    });

    it("should call slideDown", function () {
        var element = createDirective();

        spyOn(element, "slideDown");

        expect(element.slideDown).toHaveBeenCalled();
    })
});

The error message I get from the test result is: "Expected spy slideDown to have been called". I've also tried changing my test to refer to the jQuery object like below but I get the same error:

var element = createDirective();

spyOn($.fn, "slideDown");

expect($.fn.slideDown).toHaveBeenCalled();

I'm not sure why this doesn't register as a call. Is it possible to do this? If so I'd appreciate some guidance on getting this to work. Thanks