[issue28873] test_unittest failures when refleak hunting

[Nick Coghlan]

New submission from Nick Coghlan:

test_unittest currently fails for me when hunting refleaks (Fedora 25):

$ ./python -m test -R 3:3 -v test_unittest

======================================================================
ERROR: test_discover_with_init_module_that_raises_SkipTest_on_import (unittest.test.test_discovery.TestDiscovery)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ncoghlan/devel/py36/Lib/unittest/test/test_discovery.py", line 572, in test_discover_with_init_module_that_raises_SkipTest_on_import
    pickle.loads(pickle.dumps(suite, proto))
_pickle.PicklingError: Can't pickle <class 'unittest.loader.ModuleSkipped'>: attribute lookup ModuleSkipped on unittest.loader failed

======================================================================
ERROR: test_discover_with_module_that_raises_SkipTest_on_import (unittest.test.test_discovery.TestDiscovery)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ncoghlan/devel/py36/Lib/unittest/test/test_discovery.py", line 548, in test_discover_with_module_that_raises_SkipTest_on_import
    pickle.loads(pickle.dumps(suite, proto))
_pickle.PicklingError: Can't pickle <class 'unittest.loader.ModuleSkipped'>: attribute lookup ModuleSkipped on unittest.loader failed

----------------------------------------------------------------------
Ran 715 tests in 1.898s

FAILED (errors=2, skipped=7)

----------
messages: 282390
nosy: ncoghlan
priority: normal
severity: normal
stage: needs patch
status: open
title: test_unittest failures when refleak hunting
type: behavior
versions: Python 3.6

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue28873>
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