Update jQuery.hasData to always return a boolean, with unit tests.

src/data.js

@@ -22,7 +22,7 @@ jQuery.extend({
 	},
 
 	hasData: function( elem ) {
-		return !elem.nodeType || (elem[ jQuery.expando ] && !jQuery.isEmptyObject(jQuery.cache[ elem[jQuery.expando] ]));
+		return !elem.nodeType || (!!elem[ jQuery.expando ] && !jQuery.isEmptyObject(jQuery.cache[ elem[jQuery.expando] ]));
 	},
 
 	data: function( elem, name, data ) {

test/unit/data.js

@@ -78,6 +78,15 @@ test("jQuery.data", function() {
 	ok( jQuery.data( window, "BAD" ), "Make sure that the value was set." );
 });
 
+test("jQuery.hasData", function() {
+	var div = document.createElement( "div" );
+	equals( jQuery.hasData(div), false, "No data exists" );
+	jQuery.data( div, "foo", "bar" );
+	equals( jQuery.hasData(div), true, "Data exists" );
+	jQuery.removeData( div, "foo" );
+	equals( jQuery.hasData(div), false, "Data was removed" );
+});
+
 test(".data()", function() {
 	expect(5);