PyDev unittesting: How to capture text logged to a logging.Logger in "Captured Output"

Question

I am using PyDev for development and unit-testing of my Python application. As for unit-testing, everything works great except the fact that no content is logged to the logging framework. The logger is not captured by the "Captured output" of PyDev.

I'm already forwarding everything logged to the standard output like this:

import sys logger = logging.getLogger() logger.level = logging.DEBUG logger.addHandler(logging.StreamHandler(sys.stdout)) 

Nevertheless the "Captured output" does not display the stuff logged to loggers.

Here's an example unittest-script: test.py

import sys import unittest import logging  logger = logging.getLogger() logger.level = logging.DEBUG logger.addHandler(logging.StreamHandler(sys.stdout))  class TestCase(unittest.TestCase):     def testSimpleMsg(self):         print("AA")         logging.getLogger().info("BB") 

The console output is:

Finding files... done. Importing test modules ... done.  testSimpleMsg (itf.lowlevel.tests.hl7.TestCase) ... AA 2011-09-19 16:48:00,755 - root - INFO - BB BB ok  ---------------------------------------------------------------------- Ran 1 test in 0.001s  OK 

But the CAPTURED OUTPUT for the test is:

======================== CAPTURED OUTPUT ========================= AA 

Does anybody know how to capture everything that is logged to a logging.Logger during the execution of this test?

Answer 1

The issue is that the unittest runner replaces sys.stdout/sys.stderr before the testing starts, and the StreamHandler is still writing to the original sys.stdout.

If you assign the 'current' sys.stdout to the handler, it should work (see the code below).

import sys import unittest import logging  logger = logging.getLogger() logger.level = logging.DEBUG stream_handler = logging.StreamHandler(sys.stdout) logger.addHandler(stream_handler)  class TestCase(unittest.TestCase):     def testSimpleMsg(self):         stream_handler.stream = sys.stdout         print("AA")         logging.getLogger().info("BB") 

Although, a better approach would be adding/removing the handler during the test:

import sys import unittest import logging  logger = logging.getLogger() logger.level = logging.DEBUG  class TestCase(unittest.TestCase):     def testSimpleMsg(self):         stream_handler = logging.StreamHandler(sys.stdout)         logger.addHandler(stream_handler)         try:             print("AA")             logging.getLogger().info("BB")         finally:             logger.removeHandler(stream_handler) 

Answer 2

I grew tired of having to manually add Fabio's great code to all setUps, so I subclassed unittest.TestCase with some __metaclass__ing:

class LoggedTestCase(unittest.TestCase):     __metaclass__ = LogThisTestCase     logger = logging.getLogger("unittestLogger")     logger.setLevel(logging.DEBUG) # or whatever you prefer  class LogThisTestCase(type):     def __new__(cls, name, bases, dct):         # if the TestCase already provides setUp, wrap it         if 'setUp' in dct:             setUp = dct['setUp']         else:             setUp = lambda self: None             print "creating setUp..."          def wrappedSetUp(self):             # for hdlr in self.logger.handlers:             #    self.logger.removeHandler(hdlr)             self.hdlr = logging.StreamHandler(sys.stdout)             self.logger.addHandler(self.hdlr)             setUp(self)         dct['setUp'] = wrappedSetUp          # same for tearDown         if 'tearDown' in dct:             tearDown = dct['tearDown']         else:             tearDown = lambda self: None          def wrappedTearDown(self):             tearDown(self)             self.logger.removeHandler(self.hdlr)         dct['tearDown'] = wrappedTearDown          # return the class instance with the replaced setUp/tearDown         return type.__new__(cls, name, bases, dct) 

Now your test case can simply inherit from LoggedTestCase, i.e. class TestCase(LoggedTestCase) instead of class TestCase(unittest.TestCase) and you're done. Alternatively, you can add the __metaclass__ line and define the logger either in the test or a slightly modified LogThisTestCase.