$(this) inside of AJAX success not working

I am trying to change some old code which uses onclick so that I an use the $(this). The problem is that $(this) is not working when inside the success. Is there anyway to do this without setting it as a var.

$('.addToCart').click(function() {

    $.ajax({
        url: 'cart/update',
        type: 'post',
        data: 'product_id=' + $(this).attr("data-id"),
        dataType: 'json',
        success: function(json) {

            if (json['success']) {

            $(this).addClass("test");

            }   
        }
    });

});