Given the following file test_reswarn.py:

====
import unittest


class TestResourceWarning(unittest.TestCase):
    def test_it(self):
        self.assertIn("TestResourceWarning", open(__file__).read())
====

Running the test:

====
$ python -m unittest test_reswarn.py
./test_reswarn.py:6: ResourceWarning: unclosed file <_io.TextIOWrapper name='./test_reswarn.py' mode='r' encoding='UTF-8'>
  self.assertIn("TestResourceWarning", open(__file__).read())
.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK
====

When running the unit test using unittest, ResourceWarning warnings are displayed. In my experience using open("filename") without explicitly closing the file is pretty common and would usually not be an error, since the file will be closed when the reference goes out of scope (or am I wrong?).

Therefore I believe that unittest should not emit ResourceWarning warnings.

This is intentional behavior.  In the general case, resource warnings *are* bugs, since not all Python implementations do automatic cleanup.  This behavior should be controllable (I'm not even sure they *can* be turned on if python is not compiled in debug mode).

I don't see resource warnings mentioned in the TextTestRunner docs that mention the other warning controls.  It also seems like perhaps there should be a way to control warnings from the unittest command line.  So I'd say there are some improvements that can be made here, but the basic behavior is working as intended.

OK I see.

I'll just use:

python -W ignore:ResourceWarning -m unittest

I think, it is simply okay to mention about ResourceWarning being displayed. I spent something thinking and going into mechanics of how it is displayed may be an overkill for that line in unittest.rst. I'll make the change and if you see any further information can be added, please comment on it.

New changeset a8a6dc7f478b by Senthil Kumaran in branch '3.3':
Include the mention of ResourceWarning being displayed by default by the test runner.
http://hg.python.org/cpython/rev/a8a6dc7f478b

New changeset 7fc1e8095fb8 by Senthil Kumaran in branch 'default':
merge from 3.3
http://hg.python.org/cpython/rev/7fc1e8095fb8