Debugging with Test::Unit

I'd like to use a debugger ('debug', 'ruby-debug', or even irb) with
Test::Unit. So far, the standard 'debug' seems to work best with
Test::Unit, but breakpoints don't seem to work very well (compared to
'ruby-debug'). 'debug' works because it seems to stop whenever an exception
is raised (independent of whether it is rescued). 'ruby-debug' seems to
have more capability though (and breakpoints seem to work). From what I can
tell, one of these solutions would work:

- ruby-debug: have a way to stop whenever an exception is raised
- debug: breakpoints need to work more reliably
- test/unit: don't rescue AssertionFailedError

How do others use a debugger with Test::Unit?