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

Victor Stinner victor.stinner at gmail.com
Fri Jun 16 16:35:48 EDT 2017

2017-06-16 19:00 GMT+02:00 Brett Cannon <brett at python.org>:

Great idea! I had thought about doing something similar to this years ago to help diagnose when a test passes in isolation but somehow fails due to one of the bazillion of other tests that ran previously (which can be hard to narrow down if the failure is not early on in a test run).

Yeah, sometimes a test only fails if it is run after other tests. The well known issue of side effects ;-)

Each time that my script bisect_test.py script succeed to reduce the number of tests, it writes the test list on disk. So you can interrupt it the script is stuck and you consider that the output is small enough to a manual review.

Victor

On Fri, 16 Jun 2017 at 09:06 Victor Stinner <victor.stinner at gmail.com> wrote:

Hi, 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 bisecttest.py script attached to this issue: http://bugs.python.org/issue29512 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 file: ./python -m test --list-cases testos > 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 testos 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 ("ENVCHANGED" failure in regrtest). For example, a core file is dumped when running testsubprocess on FreeBSD buildbots: http://bugs.python.org/issue30448 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: http://bugs.python.org/issue30683 Victor

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