There was a recent blog post asking whether the debug framework had any unit tests and if so, where we were hiding them. Yes we do have a test suite to help protect against regressions and we hide it in the org.eclipse.jdt.debug.tests plug-in.
The majority of the tests require some implementation of the debug framework to run. We are responsible for the JDT Debugger, which is part of the SDK and implements the majority of the standard debug model. So the tests were designed to use JDT.
Until Dave brought the idea up, I had never thought of anyone using unit tests to help implement their own debugger. The current tests certainly are not set up for this style of development. I think it would be really cool to have a generic testing harness that checks the behaviour of the framework. Users could have the test harness run against their implementations of the debug interfaces/extensions. Perhaps Bug 259145 could evolve into something like that.