[Python-Dev] New work-in-progress bisection tool for the Python test suite (in regrtest)

Victor Stinner victor.stinner at gmail.com
Fri Jun 16 12:05:12 EDT 2017


Last weeks, I worked on a new tool to bisect failing tests because
it's painful to bisect manually reference leaks (I remove as much code
as possible until the code is small enough to be reviewable manually).

See the bisect_test.py script attached to this issue:

With the help of Louie Lu, I added new --list-cases option to "python
-m test", so you can now list all test cases and write it into a text

   ./python -m test --list-cases test_os > tests

I also added a new --matchfile option, to filter tests using a text
file which contains one pattern per line:

   ./python -m test --matchfile=tests test_os

fnmatch is used to match test names, so "*" joker character can be
used in test names.

My bisection tool takes a text file with the --matchfile format (one
pattern per line) and creates a random subset of tests with half of
the tests. If tests still fail, use the subset. Otherwise, create a
new random subset. Loop until the subset contains a single test
(configurable threshold, -n command line option).

The long term plan is to integrate the bisection feature directly into regrtest.

Right now, my script is hardcoded to bisect reference leak bugs, but
it should be easy to modify it to bisect other test issues like test
creating files without removing it ("ENV_CHANGED" failure in

For example, a core file is dumped when running test_subprocess on
FreeBSD buildbots:


But I'm unable to reproduce the issue on my FreeBSD. It would be nice
to be able to automate the bisection on the buildbot directly.

--list-cases and --matchfile options are now available in 2.7, 3.5,
3.6 and master (3.7) branches.

TODO: doctest tests are only partially supported, see:



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