To run pudb on test failures in the nose testing tool, you may use this script by Magnus Lie Hetland:

import pdb, pudb
from nose import main

def wrap(tb):
    return pudb.post_mortem((None, None, tb))

pdb.post_mortem = wrap

A plugin is also available for Nose. Its advantage compared to the above script is that the type and value of the exception are passed to pudb and shown with the traceback.