Python Unit Testing: Automatically Running the Debugger when a test fails

Question

Is there a way to automatically start the debugger at the point at which a unittest fails?

Right now I am just using pdb.set_trace() manually, but this is very tedious as I need to add it each time and take it out at the end.

For Example:

import unittest  class tests(unittest.TestCase):      def setUp(self):         pass      def test_trigger_pdb(self):         #this is the way I do it now         try:             assert 1==0         except AssertionError:             import pdb             pdb.set_trace()      def test_no_trigger(self):         #this is the way I would like to do it:         a=1         b=2         assert a==b         #magically, pdb would start here         #so that I could inspect the values of a and b  if __name__=='__main__':     #In the documentation the unittest.TestCase has a debug() method     #but I don't understand how to use it     #A=tests()     #A.debug(A)      unittest.main() 

Answer 1

I think what you are looking for is nose. It works like a test runner for unittest.

You can drop into the debugger on errors, with the following command:

nosetests --pdb 

Answer 2

import unittest import sys import pdb import functools import traceback def debug_on(*exceptions):     if not exceptions:         exceptions = (AssertionError, )     def decorator(f):         @functools.wraps(f)         def wrapper(*args, **kwargs):             try:                 return f(*args, **kwargs)             except exceptions:                 info = sys.exc_info()                 traceback.print_exception(*info)                  pdb.post_mortem(info[2])         return wrapper     return decorator  class tests(unittest.TestCase):     @debug_on()     def test_trigger_pdb(self):         assert 1 == 0 

I corrected the code to call post_mortem on the exception instead of set_trace.