It's common to get a random "env failed" issue when tests are run by buildbots, but changed environment variables are not logged, so the "env changed "information cannot be used to fix the issue :-/

Example:
------------------
...
0:07:32 [160/402] test_io failed (env changed) (51 sec)
0:07:33 [161/402] test_threading_local passed
...
0:13:04 [289/402/2] test_ssl failed (env changed) -- running: test_multiprocessing_spawn (119 sec)
0:13:05 [290/402/2] test_wsgiref passed -- running: test_multiprocessing_spawn (120 sec)
...
2 tests altered the execution environment:
    test_io test_ssl
------------------
http://buildbot.python.org/all/builders/AMD64%20FreeBSD%20CURRENT%20Debug%203.x/builds/932/steps/test/logs/stdio

I expected "Warning -- xxx was modfied by test_xxx" lines, but no, there is no such line. I don't know if it's related to stderr buffering or something else?

This buildbot runs tests in subprocesses.