Testing logger Messages with unittest

Question

I'd like to test logger messages without printing them to the screen in my unittests. Given this code:

 import logging
 logging.basicConfig(level=logging.ERROR)
 logger = logging.getLogger('test')
 logger.warning('this is a warning')

 # How do I see that there was a warning?

How do I look at the log records in the logger to see that there was a warning? I cannot find an iterator in Logger that would do the job.

Answer 1

You may need to use TestCase.assertLogs() context manager in such case. The documentation provides a pretty good example of what can be done with it:

with self.assertLogs('foo', level='INFO') as cm:
   logging.getLogger('foo').info('first message')
   logging.getLogger('foo.bar').error('second message')
self.assertEqual(cm.output, ['INFO:foo:first message',
                             'ERROR:foo.bar:second message'])

Inside the context manager, you can access cm.records for a list of LogRecord instances, or cm.output for a list of formatted messages