There are quite a lot regular expression tester utilities available for Eclipse. While all of them do a good job my favorite is RegExTester.
This project has not seen any updates for more than 2 years now, so some of you might consider it discontinued, I call it rock stable!
While working on my Oomph tutorials I found it really annoying that this little tool does not come with a p2 update site, so I created one and put it online. Feel free to use it for your own installations.