Captured output leaking

I recently updated to pytest 2.8 and noticed I got output which should be captured on stdout.

This is during tests which launch a subprocess via QProcess which then does logging on stderr, which is printed during the tests (see testprocess.py / quteprocess.py).

I was able to reproduce this with this example:

import pytest
from PyQt5.QtCore import QTimer


@pytest.yield_fixture(scope='module')
def timer():
    t = QTimer()
    t.setInterval(10)
    t.timeout.connect(lambda: print("foo"))
    t.start()
    yield t
    t.stop()


@pytest.mark.parametrize('x', range(1000))
def test_foo(qtbot, timer, x):
    qtbot.waitSignal(timer.timeout)

When running it with pytest 2.7.3:

============================================= test session starts ==============================================
platform linux -- Python 3.5.0 -- py-1.4.31 -- pytest-2.7.3
PyQt5 5.5.1 -- Qt runtime 5.5.1 -- Qt compiled 5.5.1
rootdir: /home/florian/proj/pytest, inifile: tox.ini
plugins: qt
collected 1000 items 

testcap2.py ...[…]...

========================================= 1000 passed in 1.16 seconds ==========================================

with 2.8.2:

============================================= test session starts ==============================================
platform linux -- Python 3.5.0, pytest-2.8.2, py-1.4.31, pluggy-0.3.1
PyQt5 5.5.1 -- Qt runtime 5.5.1 -- Qt compiled 5.5.1
rootdir: /home/florian/proj/pytest, inifile: tox.ini
plugins: qt-1.9.0
collected 1000 items 

testcap2.py .........foo
.........foo
.........foo
..........foo
...................foo
[…]

========================================= 1000 passed in 1.17 seconds ==========================================

I bisected this to https://github.com/pytest-dev/pytest/commit/c54afbe42e7e47afb7605f4bc226af92dbeda0a7 ("deprecate and warn about __multicall__ usage in hooks, refine docs about hook ordering, make hookwrappers respect tryfirst/trylast").

I also tried reproducing it without pytest-qt but it only seems to happen with pytest-qt.

I'm guessing the event processing happens after pytest already has lifted the capturing, and that commit changed something about the order things are done?

Run the provided QTimer reproduction with pytest 2.7.3 and 2.8.2, then inspect tests/integration/testprocess.py and tests/integration/quteprocess.py. Trace the hook-ordering change identified by commit c54afbe and how pytest-qt processes events and capture. Done means subprocess stderr and timer output remain captured under pytest 2.8.2.