How should I verify a log message when testing Python code under nose?

Question

I\'m trying to write a simple unit test that will verify that, under a certain condition, a class in my application will log an error via the standard logging API. I can\'t

Answer 1

If you define a helper method like this:

import logging

def capture_logging():
    records = []

    class CaptureHandler(logging.Handler):
        def emit(self, record):
            records.append(record)

        def __enter__(self):
            logging.getLogger().addHandler(self)
            return records

        def __exit__(self, exc_type, exc_val, exc_tb):
            logging.getLogger().removeHandler(self)

    return CaptureHandler()

Then you can write test code like this:

    with capture_logging() as log:
        ... # trigger some logger warnings
    assert len(log) == ...
    assert log[0].getMessage() == ...