Better warning diagnostics in unit tests

reswarn.log

WARNING  py.warnings reswarn.py:54: ResourceWarning: unclosed file <_io.TextIOWrapper name='/tmp/scratch/tmp.txt' mode='w' encoding='UTF-8'>
  subsubfunc()
Stack (most recent call last):
  File "reswarn.py", line 76, in <module>
    unittest.main()
  File "/usr/lib/python3.2/unittest/main.py", line 124, in __init__
    self.runTests()
  File "/usr/lib/python3.2/unittest/main.py", line 270, in runTests
    self.result = testRunner.run(self.test)
  File "/usr/lib/python3.2/unittest/runner.py", line 168, in run
    test(result)
  File "/usr/lib/python3.2/unittest/suite.py", line 67, in __call__
    return self.run(*args, **kwds)
  File "/usr/lib/python3.2/unittest/suite.py", line 105, in run
    test(result)
  File "/usr/lib/python3.2/unittest/suite.py", line 67, in __call__
    return self.run(*args, **kwds)
  File "/usr/lib/python3.2/unittest/suite.py", line 105, in run
    test(result)
  File "/usr/lib/python3.2/unittest/case.py", line 477, in __call__
    return self.run(*args, **kwds)
  File "/usr/lib/python3.2/unittest/case.py", line 425, in run
    self._executeTestPart(testMethod, outcome, isTest=True)
  File "/usr/lib/python3.2/unittest/case.py", line 370, in _executeTestPart
    function()
  File "reswarn.py", line 70, in test_basic
    func()
  File "reswarn.py", line 57, in func
    subfunc()
  File "reswarn.py", line 54, in subfunc
    subsubfunc()
  File "reswarn.py", line 28, in _showwarning
    logger.warning("%s", s, stack_info=1)

reswarn.py

import logging
import sys
import unittest
import warnings

#
# The following code is copied from logging/__init__.py. The only real change
# is to add stack_info=1 to the logger.warning() call.
#
_warnings_showwarning = None

def _showwarning(message, category, filename, lineno, file=None, line=None):
    """
    Implementation of showwarnings which redirects to logging, which will first
    check to see if the file parameter is None. If a file is specified, it will
    delegate to the original warnings implementation of showwarning. Otherwise,
    it will call warnings.formatwarning and will log the resulting string to a
    warnings logger named "py.warnings" with level logging.WARNING.
    """
    if file is not None:
        if _warnings_showwarning is not None:
            _warnings_showwarning(message, category, filename, lineno, file, line)
    else:
        s = warnings.formatwarning(message, category, filename, lineno, line)
        logger = logging.getLogger("py.warnings")
        if not logger.handlers:
            logger.addHandler(logging.NullHandler())
        logger.warning("%s", s, stack_info=1)

def captureWarnings(capture):
    """
    If capture is true, redirect all warnings to the logging package.
    If capture is False, ensure that warnings are not redirected to logging
    but to their original destinations.
    """
    global _warnings_showwarning
    if capture:
        if _warnings_showwarning is None:
            _warnings_showwarning = warnings.showwarning
            warnings.showwarning = _showwarning
    else:
        if _warnings_showwarning is not None:
            warnings.showwarning = _warnings_showwarning
            _warnings_showwarning = None

#
# end of code copied from logging.
#

def subsubfunc():
    f = open('/tmp/scratch/tmp.txt', 'w')

def subfunc():
    subsubfunc()

def func():
    subfunc()

class TestCase(unittest.TestCase):
    def setUp(self):
        self.saved_filters = warnings.filters
        warnings.resetwarnings()
        captureWarnings(True)

    def tearDown(self):
        captureWarnings(False)
        warnings.filters = self.saved_filters

    def test_basic(self):
        func()


if __name__ == '__main__':
    logging.basicConfig(filename='reswarn.log', filemode='w',
                        format='%(levelname)-8s %(name)s %(message)s')
    unittest.main()
    sys.exit(rc)