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bpo-29514: Check magic number for bugfix release #54

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44 changes: 44 additions & 0 deletions Lib/test/test_importlib/test_util.py
Original file line number Diff line number Diff line change
Expand Up @@ -757,5 +757,49 @@ def test_source_from_cache_path_like_arg(self):
) = util.test_both(PEP3147Tests, util=importlib_util)


class MagicNumberTests:
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Inherit from unittest.TestCase here

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I initially avoided this and followed the test machinery as I wasn't sure about directly importing importlib.util within this test module, but after looking at the way the test specialization works I don't see how this is an issue. Changed in 1e32a1b.

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Yeah, this module does some interesting things to create "real" test classes in different configurations, but we don't need those kinds of tricks for the new test.

"""
Test release compatibility issues relating to importlib
"""
def test_magic_number(self):
"""
Each python minor release should generally have a MAGIC_NUMBER
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I think it would be better to write this as a comment rather than a docstring. If you want, add a one-line docstring, but most test methods don't have docstrings.

that does not change once the release reaches candidate status.

Once a release reaches candidate status, the value of the constant
EXPECTED_MAGIC_NUMBER in this test should be changed.
This test will then check that the actual MAGIC_NUMBER matches
the expected value for the release.

In exceptional cases, it may be required to change the MAGIC_NUMBER
for a maintenance release. In this case the change should be
discussed in python-dev. If a change is required, community
stakeholders such as OS package maintainers must be notified
in advance. Such exceptional releases will then require an
adjustment to this test case.
"""
if sys.version_info.releaselevel not in ('final', 'candidate'):
return
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This can change to a unittest.skipUnless decorator on the testmethod:

@unittest.skipUnless(sys.version_info.release in ('final', 'release'), 'Only check magic number stability for release candidates and later')

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Done in 1e32a1b

EXPECTED_MAGIC_NUMBER = 3379
actual = int.from_bytes(self.util.MAGIC_NUMBER[:2], 'little')

msg = (
"Candidate and final releases require the current "
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I'd start this message with "To avoid breaking backwards compatibility with cached bytecode files that can't be automatically regenerated by the current user, ..."

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Added in 1e32a1b

"importlib.util.MAGIC_NUMBER to match the expected "
"magic number in this test. Set the expected "
"magic number in this test to the current MAGIC_NUMBER to "
"continue with the release.\n\n"
"Changing the MAGIC_NUMBER for a maintenance release "
"requires discussion in python-dev and notification of "
"community stakeholders."
)
self.assertEqual(EXPECTED_MAGIC_NUMBER, actual, msg)


Source_MagicNumberTests = util.specialize_class(
MagicNumberTests, 'Source', None, util=importlib_util
)


if __name__ == '__main__':
unittest.main()