the only testing tool I have used for GUI testing is sikuli. It works on both Windows and Mac. It is Open Source. Allows you to expand it if you wish. the work flow is based on screenshots (or partial screenshots) there you dont have to have some UI scripting language installed.
on whatever machine you are doing the testing, I would reduce the resolution down. the larger the resoultion the slower it gets as it has to parse the screen for the screenshot(s) it is looking for.
On OS X IF you have accessibility turned on you can write an applescript that says
something along the lines of
tell app to click button
or whatever
However telling that the result IS exactly what you expect is the hard part regardless.
Many tools that I’ve seen like eggPlant etc rely on comparing “good” images vs “not good” and there’s a limit to how well that can work