mocking a logging object

Peter Bengtsson

In my unittest I want to override the logger of a working module so
that it puts all logging messages in /tmp/test.log instead so that in
my unittest I can inspect that it logs things correctly. Hopefully
this "pseudo" code will explain my problem::

>>import logging, os
logging.basicConfig(filename='/tmp/real.log', level=logging.INFO)
logger = logging.getLogger('Real')
logger.info('Real stuff')
os.path.isfile('/tmp/real.log')

True

>># do the monkey patching like the unit test does
logging.basicConfig(filename='/tmp/test.log', level=logging.INFO)
logger = logging.getLogger('Test')
logger.info('Test stuff')
os.path.isfile('/tmp/test.log')

False

>>open('/tmp/real.log').read()

'INFO:Real:Real stuff\nINFO:Test:Test stuff\n'

How can I change what file the logger should write to?

Jun 27 '08 #1

Diez B. Roggisch

Peter Bengtsson wrote:

In my unittest I want to override the logger of a working module so
that it puts all logging messages in /tmp/test.log instead so that in
my unittest I can inspect that it logs things correctly. Hopefully
this "pseudo" code will explain my problem::

>>>import logging, os
logging.basicConfig(filename='/tmp/real.log', level=logging.INFO)
logger = logging.getLogger('Real')
logger.info('Real stuff')
os.path.isfile('/tmp/real.log')

True

>>># do the monkey patching like the unit test does
logging.basicConfig(filename='/tmp/test.log', level=logging.INFO)
logger = logging.getLogger('Test')
logger.info('Test stuff')
os.path.isfile('/tmp/test.log')

False

>>>open('/tmp/real.log').read()

'INFO:Real:Real stuff\nINFO:Test:Test stuff\n'

How can I change what file the logger should write to?

You should simply attach a new handler to the logger in question that logs
the data into a stream/StringIO-object for later retrieval. Then remove
that handler after the test.

Diez

Jun 27 '08 #2

Peter Bengtsson

On Jun 2, 12:34*pm, "Diez B. Roggisch" <de...@nospam.web.dewrote:

Peter Bengtsson wrote:

In my unittest I want to override the logger of a working module so
that it puts all logging messages in /tmp/test.log instead so that in
my unittest I can inspect that it logs things correctly. Hopefully
this "pseudo" code will explain my problem::

>>import logging, os
logging.basicConfig(filename='/tmp/real.log', level=logging.INFO)
logger = logging.getLogger('Real')
logger.info('Real stuff')
os.path.isfile('/tmp/real.log')

True

>># do the monkey patching like the unit test does
logging.basicConfig(filename='/tmp/test.log', level=logging.INFO)
logger = logging.getLogger('Test')
logger.info('Test stuff')
os.path.isfile('/tmp/test.log')

False

>>open('/tmp/real.log').read()

'INFO:Real:Real stuff\nINFO:Test:Test stuff\n'

How can I change what file the logger should write to?

You should simply attach a new handler to the logger in question that logs
the data into a stream/StringIO-object for later retrieval. Then remove
that handler after the test.

Diez

Thanks! I'll try that.

Jun 27 '08 #3

Peter Bengtsson

On Jun 2, 12:34*pm, "Diez B. Roggisch" <de...@nospam.web.dewrote:

Peter Bengtsson wrote:

In my unittest I want to override the logger of a working module so
that it puts all logging messages in /tmp/test.log instead so that in
my unittest I can inspect that it logs things correctly. Hopefully
this "pseudo" code will explain my problem::

>>import logging, os
logging.basicConfig(filename='/tmp/real.log', level=logging.INFO)
logger = logging.getLogger('Real')
logger.info('Real stuff')
os.path.isfile('/tmp/real.log')

True

>># do the monkey patching like the unit test does
logging.basicConfig(filename='/tmp/test.log', level=logging.INFO)
logger = logging.getLogger('Test')
logger.info('Test stuff')
os.path.isfile('/tmp/test.log')

False

>>open('/tmp/real.log').read()

'INFO:Real:Real stuff\nINFO:Test:Test stuff\n'

How can I change what file the logger should write to?

You should simply attach a new handler to the logger in question that logs
the data into a stream/StringIO-object for later retrieval. Then remove
that handler after the test.

Diez

Yes! That worked. Thank you.

Jun 27 '08 #4