It just depends on which platform you want to use. Usually each rules platform includes its own tooling/BRMS. For instance, Drools has Guvnor/Workbench and some Eclipse plugins.
I haven't used them for a while, but a few years ago, IBM ILOG JRules and FICO Blaze Advisor both had (Eclipse-based I think) IDEs for building rules management web sites. i.e. Developers would use the IDE to generate a web site. The web site would be deployed and used by business users to manage their rules. I'm pretty sure that the Pega platform follows a similar pattern.
All of the above provide a means of defining a business model, a guided editor GUI for building complex rules and a GUI for decision tables. They usually also provide some form of add-on tooling for business process workflow.
Other than that, I use JUnit for testing. But that's just my preference.