A recent sysconfig test which should have been skipped on Windows (now fixed) exposed a bug in the assertIn/assertNotIn methods. If the "container" you are testing doesn't support membership testing or iteration, such as None value when a previous call fails, the test is then an error rather than a fail.

Before:
======================================================================
ERROR: test_ldshared_value (test.test_sysconfig.TestSysConfig)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\python-dev\py3k\lib\test\test_sysconfig.py", line 285, in test_ldshar
ed_value
    self.assertIn(ldflags, ldshared)
  File "c:\python-dev\py3k\lib\unittest\case.py", line 797, in assertIn
    if member not in container:
TypeError: argument of type 'NoneType' is not iterable


I believe this should be a fail with AssertionError, rather than an error with TypeError.

======================================================================
FAIL: test_ldshared_value (test.test_sysconfig.TestSysConfig)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\python-dev\py3k\lib\test\test_sysconfig.py", line 285, in test_ldshar
ed_value
    self.assertIn(ldflags, ldshared)
AssertionError: None does not support the `in` operator



The patch adds a check that __contains__, __iter__, or __getitem__ exist on the object and fails the test if none of those are found. It also includes a few test updates.

No, assertIn is for testing for membership in a container. If you pass it something that isn't a container then it indicates an error in the test (or misuse of the assert!).

I knew there was a reason I was thinking my whole idea was slightly ridiculous...duh.