tests for other bits look ok.

this would still be much better if the tooltip size was configurable (i.e. pass to constructor with default) and tested, or at LEAST exported to a constant rather than being arbitrarily hardcoded to 13, it's good to [avoid mysterious numbers](http://c2.com/cgi/wiki?MagicNumber) in the code because it's all too easy to forget where to change things later. this line would be much better if it read `.attr("r", function(d,i) { return self.pointRadius }`or something (btw what's the idea of not showing if `i != true`?)