Simple but powerful assertion and verification of logged lines.
A simple log assertion mechanism for Python unittests.
As is vox populi, you must also test the logging calls in your programs.
logassert this is now very easy.
Awesome! How do I use it?
The same functionality is exposed in two very different ways, one that fits better the pytest semantics, the other one more suitable for classic unit tests.
All you need to do is to declare
logs in your test arguments, it works
just like any other fixture.
Then you just check (using
assert, as usual with pytest) if a specific
line is in the logs for a specific level.
def test_bleh(logs) (...) assert "The meaning of life is 42" in logs.debug
Actually, the line you write is a regular expression, so you can totally do (in case you're not exactly sure which the meaning of life is):
assert "The meaning of life is \d+" in logs.debug
The indicated string is searched to be inside the log lines, it doesn't need to be exact whole line. If you want that, just indicate it as with any regular expression:
assert "^The meaning of life is \d+$" in logs.debug
In a similar way you can also express the desire to check if it's at the beginning or at the end of the log lines.
NOTE: the message checked is the final one, after the logging system replaced all the indicated parameters in the indicated string.
If you want to verify that a text was logged, no matter at which level, just do:
assert "The meaning of life is 42" in logs.any_level
To verify that some text was NOT logged, just juse the Python's syntax! For example:
assert "A problem happened" not in logs.error
But I don't like regexes, I want the exact string
Then you just import
logassert and wrap the string
For example, in this case the
.. means exactly two dots, no regex
semantics at all:
assert Exact("The meaning of life is ..") in logs.any_level
Anyway, I liked old behaviour of searching multiple strings
Then you may want to import
logassert and wrap the
different strings you had in each call for the classic behaviour.
assert Multiple("life", "meaning", "42") in logs.any_level
What if I want to check that nothing was logged?
The simplest way to do it is to use the
NOTHING verifier that you can
assert NOTHING in logs.debug
Note that it doesn't make sense to use it by the negative (
...NOTHING not in logs...):
is no really useful at testing level to know that "something was logged", you should
improve the test to specifically verify what was logged.
Breaking the "per line barrier"
Sometimes it's useful to verify that several lines were logged, and that those lines are logged one after the other, as they build a "composite message".
To achieve that control on the logged lines you can use the
helper, that receives all the lines to verify (regexes by default, but
you can use the other helpers there):
assert Sequence( "Got 2 errors and \d+ warnings:", Exact(" error 1: foo"), Exact(" error 2: bar"), ) in logs.debug
person = "madam" item = "wallet" logger.debug("Excuse me %s, you dropped your %s", person, item)
...the following test will just pass:
assert "Excuse me .*?, you dropped your wallet" in logs.debug
However, the following will fail (different text!)...
assert "Excuse me .*?, you lost your wallet" in logs.debug
...producing this message in your tests:
assert for regex 'Excuse me .*?, you lost your wallet' check in DEBUG, failed; logged lines: DEBUG 'Excuse me madam, you dropped your wallet'
This one will also fail (different level!)...
assert "Excuse me .*?, you dropped your wallet" in logs.info
...producing this message in your tests:
assert for regex 'Excuse me .*?, you dropped your wallet' check in INFO, failed; logged lines: DEBUG 'Excuse me madam, you dropped your wallet'
A more complex example, with several log lines, and a specific assertion:
logger.info("Starting system") places = ['/tmp/', '~/temp'] logger.debug("Checking for config XYZ in all these places %s", places) logger.warning("bad config XYZ") assert "bad config XYZ" in logs.debug
See how the test failure message is super helpful:
assert for regex 'bad config XYZ' check in DEBUG, failed; logged lines: INFO 'Starting system' DEBUG "Checking for config XYZ in all these places ['/tmp/', '~/temp']" WARNING 'bad config XYZ'
What about repeated verifications?
Sometimes it's needed to verify that something if logged only once (e.g.
welcoming messages). In this cases it's super useful to use the
See the following test sequence:
def test_welcoming message(logs): logger.info("foo") # first log! it should trigger the welcoming message assert "Welcome" in logs.info logs.reset() logger.info("foo") # second log! it should NOT trigger the welcoming message assert "Welcome" not in logs.info
For classic TestCases
All you need to do is to call this module's
setup() passing the test case
instance, and the logger you want to supervise.
class MyTestCase(unittest.TestCase): """Example.""" def setUp(self): logassert.setup(self, 'mylogger')
In the example,
mylogger is the name of the logging to supervise. If
different subsystems of your code log in other loggers, this tester
Then, to use it, just call the
assertLogged method and it's family,
passing all the strings you want to find. This is the default behaviour for
def test_blah(self): (...) self.assertLoggedDebug('secret', 'life', '42')
That line will check that "secret", "life" and "42" are all logged in the same logging call, in DEBUG level.
So, if you logged this, the test will pass:
logger.debug("The secret of life, the universe and everything is %d", 42)
Note that the message checked is the one with all parameters replaced.
But if you logged any of the following, the test will fail (the first because it misses one of the string, the second because it has the wrong log level)::
logger.debug("The secret of life, the universe and everything is lost") logger.info("The secret of life, the universe and everything is 42")
What can I test?
You'll have at disposition several assertion methods:
self.assertLogged: will check that the strings were logged, no matter at which level
self.assertLoggedLEVEL(being LEVEL one of Error, Warning, Info, or Debug): will check that the strings were logged at that specific level.
self.assertNotLogged: will check that the strings were NOT logged, no matter at which level
self.assertNotLoggedLEVEL(being LEVEL one of Error, Warning, Info, or Debug): will check that the strings were NOT logged at that specific level.
If you need help, or have any question, or found any issue, please open a ticket here.
Thanks in advance for your time.
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