caplog: Use 'session' scope

[MarBra]

Hi pytest-experts :)

i like to use the caplog fixture in another fixture with session scope:

import pytest
import logging

@pytest.fixture(scope='session')
def my_log(caplog):
    caplog.set_level(logging.INFO)

def test_foo(my_log):
    pass

This results in the following error:
ScopeMismatch: You tried to access the 'function' scoped fixture 'caplog' with a 'session' scoped request object, involved factories

[RonnyPfannschmidt]

thats currently not supported

[Zac-HD]

You can't use function-scoped fixtures in session-scoped fixtures, because there's no correct time to create or destroy the result! caplog specifically basically has to be function-scoped to avoid weird interactions, too. See e.g. #2704.

Fortunately there's an easy fix here - just define my_log as a function-scoped fixture and you'll be fine.

[Forty-Bot]

This is still an issue. Sometimes you need to capture log output and you can't make the fixture session-scoped (such as when it involves a lot of work to set up). For these cases, I present the following workaround:

request.node.add_report_section = lambda *args: None
logging_plugin = request.config.pluginmanager.getplugin('logging-plugin')
for _ in logging_plugin.pytest_runtest_setup(request.node):
   caplog = pytest.LogCaptureFixture(request.node, _ispytest=True)
   # do whatever you want with caplog

This can also be trivially extended as a context manager. You may want to call _finalize if you modify the log level.

[nickeldan]

@Forty-Bot, where does that code get put?

[Forty-Bot]

Anywhere you want, really. I made it a context manager so I can use it with with.