It seems there is a problem with at `url: "/wp-admin/admin-ajax.php"`, instead try adding the full path:

    function addajaxurl() {
        wp_localize_script( 'frontend-ajax', 'frontendajax', array( 'ajaxurl' => admin_url( 'admin-ajax.php' )));
    }
    add_action( 'wp_enqueue_scripts', 'addajaxurl' );

and call the variable in your ajax function:

            jQuery.ajax({
                type:"POST",
                action: "my_test_action",
                url: ajaxurl,
                data: newFormChange,
                success:function(data){
                    console.log(data);
                }
            });