Some assert functions are renamed/missing in various Python versions

[Adam Harwell]

Documentation for unittest in PY2/PY3:

https://docs.python.org/2/library/unittest.html#test-cases (see functions noted with "New in version 2.7.")
https://docs.python.org/3/library/unittest.html#test-cases (see functions noted with "New in version 3.x.")

For example, to do a fuzzy-comparison of two collections:

Python 2.7 unittest includes unittest.TestCase.assertItemsEqual( ).
Python 3.2+ unittest includes unittest.TestCase.assertCountEqual( ).
Python 2.6 unittest does not include either of these functions.

As far as I can tell, there's nothing in `six` to handle this. I've had to work around the problem in my own classes that implement testtools.TestCase, using the following:

if hasattr(testtools.TestCase, 'assertItemsEqual'):
    # If this function is available, do nothing (PY27)
    pass
elif hasattr(testtools.TestCase, 'assertCountEqual'):
    # If this function is available, alias it (PY32+)
    assertItemsEqual = testtools.TestCase.assertCountEqual
else:
    # If neither is available, make our own version (PY26, PY30-31?)
    def assertItemsEqual(self, expected_seq, actual_seq, msg=None):
        # Custom implementation is here

I believe this should be handled at the testtools layer.

Expected functionality for any version of Python (assuming the best option is to just make both names available):

self.assertItemsEqual(list1, list2) -> does comparison
self.assertCountEqual(list1, list2) -> does comparison

Actual functionality:

Py26: self.assertItemsEqual(list1, list2) -> exception raised, no method found
Py27: self.assertItemsEqual(list1, list2) -> does comparison
Py31: self.assertItemsEqual(list1, list2) -> exception raised, no method found
Py32+: self.assertItemsEqual(list1, list2) -> exception raised, no method found

Py26: self.assertCountEqual(list1, list2) -> exception raised, no method found
Py27: self.assertCountEqual(list1, list2) -> exception raised, no method found
Py31: self.assertCountEqual(list1, list2) -> exception raised, no method found
Py32+: self.assertCountEqual(list1, list2) -> does comparison

[Adam Harwell (adam-harwell)]

Most of the functions that are missing from unittest in Python 2.6.x are available via unittest2.

[Robert Collins (lifeless)]

Sorry, what is the bug?

[Adam Harwell (adam-harwell)]

Inheriting from testtools.TestCase gives access to certain assert functions that are either missing or behave differently in different python versions, which makes writing polyglot code (like in OpenStack and many other projects) difficult. The only place I can think of that this fix would go is in testtools. See the original description for details on specifics. I'm also on Freenode as rm_you if you'd like me to run through the issue.

[Adam Harwell (adam-harwell)]

Ok, per our conversation on IRC, I have re-tested and it does look like this was resolved. Thanks!