python - 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)