pytest

py.test is a simple yet powerful tool that allows you to run tests. It may be useful not only for big projects but even for one-off scripts.

Let's say you write a small utility to parse some log, and you have a function to detect GET requests.

def is_get(line):
    return re.search(r'\bGET\b', line)

To test it you may put some debug statements in your script, copy the function to another file or Python shell and run it manually, or create a stand-alone test script. Or you may just define test_is_get along is_get that doesn't interfere with your script unless it is executed with py.test.

def test_is_get():
    assert is_get('12:00 GET url')
    assert is_get('00:00 url GET params')
    assert not is_get('07:00 GETTER restart')

Once the script is started with py.test log_parser.py, all test_* will be executed. This way you can actually have two modes to run your script: with python to parser log or with py.test to test some things you want to be tested.