Add simple error handling for domEqual method (was failing for menu, output not helpful).

Author: jzaefferer

tests/unit/testsuite.js

@@ -75,6 +75,10 @@ window.domEqual = function( selector, modifier, message ) {
 	var attributes = ["class", "role", "id", "tabIndex", "aria-activedescendant"];
 
 	function extract(value) {
+		if (!value || !value.length) {
+			QUnit.push( false, actual, expected, "domEqual failed, can't extract " + selector + ", message was: " + message );
+			return;
+		}
 		var result = {};
 		result.nodeName = value[0].nodeName;
 		$.each(attributes, function(index, attr) {