Mocking Javascript objects (specifically YUI)

I'm trying to mock YUI for javascript testing. I want to mock a datatable, but im not sure how to do it.

Something like

 YAHOO.widget.DataTable = function(){

  };

so latter I could do some开发者_如何学Gothing like

   assert.that(returnedDatatable, isOfType(YAHOO.widget.DataTable));

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My answer: js mockito or don't use YUI :)