python - Logging within pytest tests

Question

I would like to put some logging statements within test function to examine some state variables.

I have the following code snippet:

import pytest,os
import logging

logging.basicConfig(level=logging.DEBUG)
mylogger = logging.getLogger()

#############################################################################

def setup_module(module):
    ''' Setup for the entire module '''
    mylogger.info('Inside Setup')
    # Do the actual setup stuff here
    pass

def setup_function(func):
    ''' Setup for test functions '''
    if func == test_one:
        mylogger.info(' Hurray !!')

def test_one():
    ''' Test One '''
    mylogger.info('Inside Test 1')
    #assert 0 == 1
    pass

def test_two():
    ''' Test Two '''
    mylogger.info('Inside Test 2')
    pass

if __name__ == '__main__':
    mylogger.info(' About to start the tests ')
    pytest.main(args=[os.path.abspath(__file__)])
    mylogger.info(' Done executing the tests ')

I get the following output:

[bmaryada-mbp:/Users/bmaryada/dev/platform/main/proto/tests/tpch $]python minitest.py
INFO:root: About to start the tests 
======================================================== test session starts =========================================================
platform darwin -- Python 2.6.2 -- pytest-2.0.0
collected 2 items 

minitest.py ..

====================================================== 2 passed in 0.01 seconds ======================================================
INFO:root: Done executing the tests 

Notice that only the logging messages from the '__name__ == __main__' block get transmitted to the console.

Is there a way to force pytest to emit logging to console from test methods as well?

Answer 1

Since version 3.3, pytest supports live logging, meaning that all the log records emitted in tests will be printed to the terminal immediately. The feature is documented under Live Logs section. Live logging is disabled by default; to enable it, set log_cli = 1 in the pyproject.toml¹ or pytest.ini² config. Live logging supports emitting to terminal and file; the relevant options allow records customizing:

terminal:

• log_cli_level
• log_cli_format
• log_cli_date_format

file:

• log_file
• log_file_level
• log_file_format
• log_file_date_format

Note: log_cli flag can't be passed from command line and must be set in pytest.ini. All the other options can be both passed from command line or set in the config file. As pointed out by Kévin Barré in this comment, overriding ini options from command line can be done via the -o/--override option. So instead of declaring log_cli in pytest.ini, you can simply call:

$ pytest -o log_cli=true ...

Examples

Simple test file used for demonstrating:

# test_spam.py

import logging

LOGGER = logging.getLogger(__name__)


def test_eggs():
    LOGGER.info('eggs info')
    LOGGER.warning('eggs warning')
    LOGGER.error('eggs error')
    LOGGER.critical('eggs critical')
    assert True

As you can see, no extra configuration needed; pytest will setup the logger automatically, based on options specified in pytest.ini or passed from command line.

Live logging to terminal, INFO level, fancy output

Configuration in pyproject.toml:

[tool.pytest.ini_options]
log_cli = true
log_cli_level = "INFO"
log_cli_format = "%(asctime)s [%(levelname)8s] %(message)s (%(filename)s:%(lineno)s)"
log_cli_date_format = "%Y-%m-%d %H:%M:%S"

The identical configuration in legacy pytest.ini:

[pytest]
log_cli = 1
log_cli_level = INFO
log_cli_format = %(asctime)s [%(levelname)8s] %(message)s (%(filename)s:%(lineno)s)
log_cli_date_format=%Y-%m-%d %H:%M:%S

Running the test:

$ pytest test_spam.py
=============================== test session starts ================================
platform darwin -- Python 3.6.4, pytest-3.7.0, py-1.5.3, pluggy-0.7.1 -- /Users/hoefling/.virtualenvs/stackoverflow/bin/python3.6
cachedir: .pytest_cache
rootdir: /Users/hoefling/projects/private/stackoverflow/so-4673373, inifile: pytest.ini
collected 1 item

test_spam.py::test_eggs
---------------------------------- live log call -----------------------------------
2018-08-01 14:33:20 [    INFO] eggs info (test_spam.py:7)
2018-08-01 14:33:20 [ WARNING] eggs warning (test_spam.py:8)
2018-08-01 14:33:20 [   ERROR] eggs error (test_spam.py:9)
2018-08-01 14:33:20 [CRITICAL] eggs critical (test_spam.py:10)
PASSED                                                                        [100%]

============================= 1 passed in 0.01 seconds =============================

Live logging to terminal and file, only message & CRITICAL level in terminal, fancy output in pytest.log file

Configuration in pyproject.toml:

[tool.pytest.ini_options]
log_cli = true
log_cli_level = "CRITICAL"
log_cli_format = "%(message)s"

log_file = "pytest.log"
log_file_level = "DEBUG"
log_file_format = "%(asctime)s [%(levelname)8s] %(message)s (%(filename)s:%(lineno)s)"
log_file_date_format = "%Y-%m-%d %H:%M:%S"

The identical configuration in legacy pytest.ini:

[pytest]
log_cli = 1
log_cli_level = CRITICAL
log_cli_format = %(message)s

log_file = pytest.log
log_file_level = DEBUG
log_file_format = %(asctime)s [%(levelname)8s] %(message)s (%(filename)s:%(lineno)s)
log_file_date_format=%Y-%m-%d %H:%M:%S

Test run:

$ pytest test_spam.py
=============================== test session starts ================================
platform darwin -- Python 3.6.4, pytest-3.7.0, py-1.5.3, pluggy-0.7.1 -- /Users/hoefling/.virtualenvs/stackoverflow/bin/python3.6
cachedir: .pytest_cache
rootdir: /Users/hoefling/projects/private/stackoverflow/so-4673373, inifile: pytest.ini
collected 1 item

test_spam.py::test_eggs
---------------------------------- live log call -----------------------------------
eggs critical
PASSED                                                                        [100%]

============================= 1 passed in 0.01 seconds =============================

$ cat pytest.log
2018-08-01 14:38:09 [    INFO] eggs info (test_spam.py:7)
2018-08-01 14:38:09 [ WARNING] eggs warning (test_spam.py:8)
2018-08-01 14:38:09 [   ERROR] eggs error (test_spam.py:9)
2018-08-01 14:38:09 [CRITICAL] eggs critical (test_spam.py:10)

---

¹ pyproject.toml supported since version 6.0 and is the best option IMO. See PEP 518 for the specs.

² Although you can also configure pytest in setup.cfg under the [tool:pytest] section, don't be tempted to do that when you want to provide custom live logging format. Other tools reading setup.cfg might treat stuff like %(message)s as string interpolation and fail. The best choice is using pyproject.toml anyway, but if you are forced to use the legacy ini-style format, stick to pytest.ini to avoid errors.