JavaScript code in iframe doesn't work

Question

I have an iframe which is created after loading page. (main DOM)

var object_preview = $('#preview');

var iframe = $('<iframe id="preview_frame">'),
    iframe_body,
    iframe_head;

object_preview.html(iframe);

setTimeout(function() {
   var doc = iframe[0].contentWindow.document;
   iframe_body = $('body', doc);
   iframe_head = $('head', doc);
}, 1);

When you click on a button, in the iframe head inserted JS-code (jQuery), which must be executed within the iframe DOM.

$('#run').click(function() {
        iframe_body.append('<script type="text/javascript">\
                $(document).ready(function() {\
                        $(".test").click(function() { alert(true); });\
                });\           
        </script>');
});

Now it doesn't work. How to implement it?

Element with class .test is within iframe DOM.

HTML structure:

Thanks in advance.