[Python-Dev] Allowing to run certain regression tests in subprocesses (original) (raw)

Eli Bendersky eliben at gmail.com
Sun Aug 4 01:36:50 CEST 2013

Hi All,

Today the issue of cross-test global env dependencies showed its ugly head again for me. I recall a previous discussion (http://mail.python.org/pipermail/python-dev/2013-January/123409.html) but there were many more over the years.

The core problem is that some tests modify the global env (particularly importing modules) and this sometimes has adverse effects on other tests, because test.regrtest runs all tests in a single process. In the discussion linked above, the particular culprit test__all__ was judged as a candidate to be moved to a subprocess.

I want to propose adding a capability to our test harness to run specific tests in subprocesses. Each test will have some simple way of asking to be run in a subprocess, and regrtest will concur (even when running -j1). test__all__ can go there, and it can help solve other problems.

My particular case is trying to write a test for http://bugs.python.org/issue14988 - wherein I have to simulate a situation of non-existent pyexpat. It's not hard to write a test for it, but when run in tandem with other tests (where C extensions loaded pyexpat) it becomes seemingly impossible to set up. This should not be the case - there's nothing wrong with wanting to simulate this case, and there's nothing wrong in Python and the stdlib - it's purely an artifact of the way our regression suite works.

Thoughts?

Eli

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