Here are several solutions to run unit tests in Python.

Python standard library:
- doctest: http://docs.python.org/lib/module-doctest.html
- unittest/PyUnit: http://pyunit.sourceforge.net/pyunit.html

Third-party:
- TestOOB: http://testoob.sourceforge.net
- py.test: http://codespeak.net/py/dist/test.html
- nose: http://www.somethingaboutorange.com/mrl/projects/nose/
- nose plugins repository: http://nose-plugins.jottit.com/

Articles comparing unittest, doctest and py.test:
http://agiletesting.blogspot.com/2005/01/python-unit-testing-part-1-unit...
http://agiletesting.blogspot.com/2005/01/python-unit-testing-part-2-doct...
http://agiletesting.blogspot.com/2005/01/python-unit-testing-part-3-pyte...

Presentation about nose: http://us.pycon.org/common/2008/talkdata/PyCon2008/079/nose_pycon08.pdf