Assert that logging has been called with specific string - python-2.7

Question

I'm trying to use unittest to test some functions of a SimpleXMLRPCServer I made. Togethere with Mock, I'm now trying to assert that a specific message has been logged when an if statement is reached, but I can't get it to work. I've tried implementing various answers I found here on StackOverflow or by Googling, but still no luck. The calls I make in the Test Case are as follows:
def test_listen_for_tasks(self):
el = {'release': 'default', 'component': None}
for i in range(50):
self.server._queue.put(el)
ServerThread.listen_for_tasks(self.server, 'bla', 'blabla')
with mock.patch('queue_server.logging') as mock_logging:
mock_logging.warning.assert_called_with('There are currently {}'
' items in the queue'.format(
str(len(self.server._queue.queue))))
The function in the server is as follows:
def listen_for_tasks(self, release, component):
item = {'release': release, 'component': component}
for el in list(self._queue.queue):
if self.is_request_duplicate(el, item):
logger.debug('Already have a request'
' for this component: {}'.format(item))
return
self._queue.put(item, False)
if len(self._queue.queue) > 50:
logger.warning('There are currently {}'
' items in the queue'.format(
str(len(self._queue.queue))))
Any idea why this is not working? I'm new to unit testing in Python and asserting that a logger has done something seems the biggest problem one could face, so I might have screwed up with something really simple in the code. Any kind of help will be greatly appreciated!
EDIT: for completeness, here's the test output and failure:
.No handlers could be found for logger "queue_server"
F
FAIL: test_listen_for_tasks (__main__.TestQueueServer)
Traceback (most recent call last):
File "artifacts_generator/test_queue_server.py", line 46, in test_listen_for_tasks
str(len(self.server._queue.queue))))
File "/home/lugiorgi/Desktop/Code/publisher/env/local/lib/python2.7/site-packages/mock/mock.py", line 925, in assert_called_with
raise AssertionError('Expected call: %s\nNot called' % (expected,))
AssertionError: Expected call: warning('There are currently 51 items in the queue')
Not called
Ran 2 tests in 0.137s
FAILED (failures=1)

Answer 1

Since python 3.4 you can use unittest.TestCase class method assertLogs
import logging
import unittest
class LoggingTestCase(unittest.TestCase):
def test_logging(self):
with self.assertLogs(level='INFO') as log:
logging.info('Log message')
self.assertEqual(len(log.output), 1)
self.assertEqual(len(log.records), 1)
self.assertIn('Log message', log.output[0])

Answer 2

You need to first mock the object, then call the function you want to test.
When mocking the object, you also need to provide the full package and object/function name of the object you are mocking, not a variable name.
Finally, it's often more convenient to use the decorator form of patch.
So, for example:
logger = logging.getLogger(__name__)
def my_fancy_function():
logger.warning('test')
#patch('logging.Logger.warning')
def test_my_fancy_function(mock):
my_fancy_function()
mock.assert_called_with('test')
# if you insist on using with:
def test_my_fancy_function_with_with():
with patch('logging.Logger.warning') as mock:
my_fancy_function()
mock.assert_called_with('test')