Well, all of a sudden last night this last command was failing with errors such as:
error: invalid Python installation:
unable to open /tmp/python-buildbot/local/lib/python2.6/config/Makefile
(No such file or directory)
This proved to be was a transient error, due to some recent checkins that modified the release numbers in the python svn trunk from 2.5 to 2.6. This issue was fixed within an hour, but the interesting thing to me was that, while this step was failing in the Pybots Twisted tests, the Python builbots running the Python-specific unit tests against the trunk were merrily chugging along, green and happy (at least on Unix platforms). This was of course to be expected, since nothing major changed as far as the internal Python unit tests were concerned. However, when running a functional test involving the newly-built Python binary -- and in my case that functional test consisted simply in running "python setup.py install" on some packages -- things started to break.
Lesson learned? Always make sure you test your application from the outside in, by exercising it as a user would. Unit tests are necessary (indeed, they are essential), but they are not sufficient by any means. A 'holistic' test strategy takes into consideration both white-box-type unit tests, and black-box-type functional tests. Of course, the recommended way of running all these types of tests is via a continuous integration tool such as buildbot.