How can I use jQuery validation with the "chosen" plugin?

jQuery validation isn't going to pick up elements that are hidden, but you can force it to validate individual elements. Bit of a hack, but the following will work:

$('form').on('submit', function(e) {
    if(!$('[name="test2"]').valid()) {
        e.preventDefault();
    }
});  

To select only "chosen" elements you can use $('.chzn-done')

jQuery validate ignores the hidden element, and since the Chosen plugin adds visibility:hidden attribute to the select, try:

$.validator.setDefaults({ ignore: ":hidden:not(select)" }) //for all select

OR

$.validator.setDefaults({ ignore: ":hidden:not(.chosen-select)" }) //for all select having class .chosen-select

Add this line just before validate() function. It works fine for me.