Non-initial conftest.py not run with output capturing.

I normally run my test suite using the -n <num> option. My setup.cfg was previously set to pass a fixed list of paths as arguments to py.test via the addopts setting. I changed setup.cfg to no longer use a fixed list of paths (instead using the python_files glob option) in order to allow paths to be specified normally. After this change, I found that output from the logging module was no longer captured.

The logging module is initialized with basicConfig upon import of a log module inside the application package. This is unavoidable. The log module is indirectly imported by a conftest.py module. This is not unavoidable, just very inconvenient to work around; besides, I want to see the log output along with the results of failing tests.

Further investigation yielded some confusing results.

To reproduce the behavior, I created a test suite structured like this:

tests/
  foo/
    conftest.py
    test_foo.py
 bar/
    test_bar.py

No setup.cfg or similar is present.

foo/conftest.py initializes the logging module using basicConfig. Both foo/test_foo.py and bar/test_bar.py contain a test function that calls the logging module to log a single message, "Hello World". Under certain conditions, the "Hello World" message is not captured for any test, but sent to stderr instead. I have narrowed down those conditions to these invocations of py.test with capturing results:

• py.test without -n <num>, regardless of other arguments: Captured
• py.test -n 3 without other arguments: Not captured
• py.test -n 3 tests: Not captured
• py.test -n 3 tests/foo: Captured
• py.test -n 3 tests/foo/test_foo.py: Captured
• py.test -n 3 tests/bar: Captured
• py.test -n 3 tests/bar/test_bar.py: Captured

Start by reproducing the listed invocations with the tests/foo/conftest.py fixture and compare logging capture for tests/foo and tests/bar. Read the pytest-xdist handling around distributed test collection and output capture. Done means logging from both tests is captured consistently when running the suite with -n 3.