py.test logging control

Question

We have recently switched to py.test for python testing (which is fantastic btw). However, I'm trying to figure out how to control the log output (i.e. the built-in python logging module). We have pytest-capturelog installed and this works as expected and when we want to see logs we can pass --nologcapture option.

However, how do you control the logging level (e.g. info, debug etc.) and also filter the logging (if you're only interested in a specific module). Is there existing plugins for py.test to achieve this or do we need to roll our own?

Thanks, Jonny

Answer 1

Installing and using the pytest-capturelog plugin could satisfy most of your pytest/logging needs. If something is missing you should be able to implement it relatively easily.

Answer 2

As Holger said you can use pytest-capturelog:

def test_foo(caplog):
    caplog.setLevel(logging.INFO)
    pass

If you don't want to use pytest-capturelog you can use a stdout StreamHandler in your logging config so pytest will capture the log output. Here is an example basicConfig

logging.basicConfig(level=logging.DEBUG, stream=sys.stdout)

Answer 3

A bit of a late contribution, but I can recommend pytest-logging for a simple drop-in logging capture solution. After pip install pytest-logging you can control the verbosity of the your logs (displayed on screen) with

$ py.test -s -v tests/your_test.py
$ py.test -s -vv tests/your_test.py
$ py.test -s -vvvv tests/your_test.py

etc... NB - the -s flag is important, without it py.test will filter out all the sys.stderr information.

Answer 4

Pytest now has native support for logging control via the caplog fixture; no need for plugins.

You can specify the logging level for a particular logger or by default for the root logger:

import pytest

def test_bar(caplog):
    caplog.set_level(logging.CRITICAL, logger='root.baz')

Pytest also captures log output in caplog.records so you can assert logged levels and messages. For further information see the official documentation here and here.