I suppose this is due to the fact that no released version of Twisted is pip installable on Python 3.3 but you also don't want to change requirements-dev.txt to refer to a trunk snapshot version?

Hrmph.  Kind of a mess but I guess it will be resolveable if Twisted ever manages to get another release out.

FWIW if you used "setup.py test" then you could inspect the Python runtime version and add the correct dependency to the `install_requires` `setup()` argument.