On Sat, Dec 29, 2012 at 5:34 PM, Nick Coghlan <ncogh...@gmail.com> wrote:
> On Sun, Dec 30, 2012 at 10:46 AM, Benjamin Peterson <benja...@python.org> > wrote: > > 2012/12/29 Eli Bendersky <eli...@gmail.com>: > >> Hi, > >> > >> This came up while investigating some test-order-dependency failures in > >> issue 16076. > >> > >> test___all__ goes over modules that have `__all__` in them and does > 'from > >> <module> import *' on them. This leaves a lot of modules in sys.modules, > >> which may interfere with some tests that do fancy things with > sys,modules. > >> In particular, the ElementTree tests have trouble with it because they > >> carefully set up the imports to get the C or the Python version of etree > >> (see issues 15083 and 15075). > >> > >> Would it make sense to save the sys.modules state and restore it in > >> test___all__ so that sys.modules isn't affected by this test? > > > > Sounds reasonable to me. > > I've tried this as an inherent property of regrtest before (to resolve > some problems with test_pydoc), and it didn't work - we have too many > modules with non-local side effects (IIRC, mostly related to the copy > and pickle registries). > > Given that it checks the whole standard library, test___all__ is > likely to run into the same problem. > > Yes, I'm running into all kinds of weird problems when saving/restoring sys.modules around test___all__. This is not the first time I get to fight this test-run-dependency problem and it's very frustrating. This may be a naive question, but why don't we run the tests in separate interpreters? For example with -j <N> we do (which creates all kinds of strange intermittent problems depending on which tests got bundled into the same process). Is this a matter of performance? Because that would help get rid of these dependencies between tests, which would probably save core devs some work and headache. After all, since a lot of the interpreter state is global (for example sys.modules), does it not make sense to run each test in a clean environment? Many tests do fancy things with the global environment which makes them difficult to keep clean and separate. > Hence test.support.import_fresh_module - it can ensure you get the > module you want, regardless of the preexisting contents of > sys.modules. ( > http://docs.python.org/dev/library/test#test.support.import_fresh_module) > Yes, this is the solution currently used in test_xml_etree. However, once pickling tests are added things stop working. Pickle uses __import__ to import the module a class belongs to, bypassing all such trickery. So if test___all__ got _elementtree into sys.modules, pickle's __import__ finds it even if all the tests in test_xml_etree manage to ignore it for the Python version because they use import_fresh_module. Eli
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