The existing run_tests.py script is a non-starter with python3, so if we want to even look at adding python3 support to Roundup the run_tests.py script would need to be updated to add python3 support. This could be done, but also begs the question of why are we maintaining our own test runner script? Why not just push that maintenance burden off to some other project (ie. pytest)?
I personally find the documentation for the existing script ('run_tests.py -h') a bit confusing, I'm not sure if I have ever figured out how to run a single test case using the existing script, and some options don't behave as expected (ie. 'run_tests.py --dir test' works as one might expect, but 'run_tests.py --dir test/' doesn't).
There are also a number of benefits that adopting pytest could provide (less boilerplate, fixtures, using 'assert', etc.) if we were to fully embrace it, but the one nice benefit I have included in the current patchset is the support for test skipping decorators it brings to python2.6 (not available in unittest before python2.7). When running tests you now know how may tests have been skipped (and why), instead of just being told some tests won't be run.
If the consensus is to use another tool, then I am OK with that.