Speaking of using other tools for testing and prototyping, there are REPLs available for Cocoa.<p>My personal favorite is Nu[1] with Nutronic[2], though you can do similar things with MacRuby and PyObjC.<p>[1] <a href="http://programming.nu/" rel="nofollow">http://programming.nu/</a><p>[2] <a href="http://itfrombit.github.com/nutron/" rel="nofollow">http://itfrombit.github.com/nutron/</a>