I'm trying to use pytest to test if my function is logging the expected text, such as addressed this question (the pyunit equivalent would be assertLogs). Following the pytest logging documentation, I am passing the caplog
fixture to the tester. The documentation states:
Lastly all the logs sent to the logger during the test run are made available on the fixture in the form of both the logging.LogRecord instances and the final log text.
The module I'm testing is:
import logging
logger = logging.getLogger(__name__)
def foo():
logger.info("Quinoa")
The tester is:
def test_foo(caplog):
from mwe16 import foo
foo()
assert "Quinoa" in caplog.text
I would expect this test to pass. However, running the test with pytest test_mwe16.py
shows a test failure due to caplog.text
being empty:
============================= test session starts ==============================
platform linux -- Python 3.7.3, pytest-5.3.0, py-1.8.0, pluggy-0.13.0
rootdir: /tmp
plugins: mock-1.12.1, cov-2.8.1
collected 1 item
test_mwe16.py F [100%]
=================================== FAILURES ===================================
___________________________________ test_foo ___________________________________
caplog = <_pytest.logging.LogCaptureFixture object at 0x7fa86853e8d0>
def test_foo(caplog):
from mwe16 import foo
foo()
> assert "Quinoa" in caplog.text
E AssertionError: assert 'Quinoa' in ''
E + where '' = <_pytest.logging.LogCaptureFixture object at 0x7fa86853e8d0>.text
test_mwe16.py:4: AssertionError
============================== 1 failed in 0.06s ===============================
Why is caplog.text
empty despite foo()
sending text to a logger? How do I use pytest
such that caplog.text
does capture the logged text, or otherwise verify that the text is being logged?
By setting the log_cli configuration option to true , pytest will output logging records as they are emitted directly into the console. You can specify the logging level for which log records with equal or higher level are printed to the console by passing --log-cli-level .
Live logging is disabled by default; to enable it, set log_cli = 1 in the pyproject. toml 1 or pytest. ini 2 config.
A logger has three main fields: Propagate: Decides whether a log should be propagated to the logger's parent. By default, its value is True. A level: Like the log handler level, the logger level is used to filter out “less important” logs.
The documentation is unclear here. From trial and error, and notwithstanding the "all the logs sent to the logger during the test run are made available" text, it still only captures logs with certain log levels. To actually capture all logs, one needs to set the log level for captured log messages using caplog.set_level
or the caplog.at_level
context manager, so that the test module becomes:
import logging
def test_foo(caplog):
from mwe16 import foo
with caplog.at_level(logging.DEBUG):
foo()
assert "Quinoa" in caplog.text
Now, the test passes:
============================= test session starts ==============================
platform linux -- Python 3.7.3, pytest-5.3.0, py-1.8.0, pluggy-0.13.0
rootdir: /tmp
plugins: mock-1.12.1, cov-2.8.1
collected 1 item
test_mwe16.py . [100%]
============================== 1 passed in 0.04s ===============================
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