In short, TestWise Mac is built on an open-source library which depends on Ruby 1.8. You might wonder why not upgrade 2.0? We would like to, however, the open-source library was suspended a few years ago. There is a plan to re-develop TestWise for Mac from scratch, as you see, this requires effort.
TestWise Mac (beta) works, but not stable as we like. It is usable though, we wrote thousands of tests for our web apps, mostly on TestWise Mac. The revenue of TestWise licenses will be used for funding next development. If you like TestWise, please buy TestWise or tell others.
Back to your question, currently TestWise Mac relies on Ruby 1.8 installed under /System/Library/Frameworks/Ruby.framework/Versions/1.8