Session fixture keeps frames of other fixtures alive #2981
Description
Consider this test file:
import pytest
import weakref
class SomeObj:
def __init__(self, name):
self.name = name
def __repr__(self):
return '<SomeObj "{}">'.format(self.name)
ref = None
session_ref = None
@pytest.fixture(scope='session')
def session_fix():
global session_ref
session_obj = SomeObj('session')
session_ref = weakref.ref(session_obj)
return session_obj
@pytest.fixture
def fix(session_fix):
global ref
obj = SomeObj('local')
ref = weakref.ref(obj)
return obj
def test1(fix):
assert ref() is fix
def test2():
assert ref() is NoneThis fails with:
============================= test session starts =============================
platform win32 -- Python 3.6.3, pytest-3.3.1.dev26+gfdfc194, py-1.5.2, pluggy-0.6.0 -- c:\sybil\.env36\scripts\python.exe
cachedir: .cache
rootdir: C:\pytest\.tmp, inifile: pytest.ini
collected 2 items
test_leak.py::test1 PASSED [ 50%]
test_leak.py::test2 FAILED [100%]
================================== FAILURES ===================================
____________________________________ test2 ____________________________________
def test2():
> assert ref() is None
E assert <SomeObj "local"> is None
E + where <SomeObj "local"> = ref()
test_leak.py:31: AssertionError
===================== 1 failed, 1 passed in 0.04 seconds ======================
So for some reason the object created in fix is being kept alive after test1 has finished. This is caused by session_fix and can be verified by changing test1 to no longer require session_fix in which case both tests pass.
This seems to reproduce the errors reported in #2968 and #2970 because both tests pass in 3.2.5. 😓