Friday, December 9, 2011

Moving to Nose..

We've started to have our developers use Nose, a much more powerful unit test discovery package for Python. For one, in order to generate JUnit XML outputs for Hudson/Jenkins, the test runner comes with a --with-xunit command that lets you dump these results out.

Here are a few things that might help you get adjusted to using Nose:

1. As mentioned in the Testing Efficiently with Nose tutorial, the convention is slightly different for running tests has changed. The format has changed:

python test app.tests:YourTestCaseClass
python test app.tests:YourTestCaseClass.your_test_method

One way to force the test results to use the same format is to create a class that inherits from unittest that overrides the __str__, __id__, and shortDescription methods. The __str__() method is used by the Django test runner to display what tests are running and which ones have failed, enabling you to copy/paste the test to re-run the test. The __id__() method is used by the XUnit plug-in to generate the test name, enabling you to swap out the class name with the Nose convention. Finally, the shortDescription() will prevent docstrings from replacing the test name when running the tests.

class BaseTestCase(unittest.TestCase):

def __str__(self):
# Use Nose testing format (colon to differentiate between module/class name)

if 'django_nose' in settings.INSTALLED_APPS or 'nose' in settings.TEST_RUNNER.lower():
return "%s:%s.%s" % (self.__module__, self.__class__.__name__, self._testMethodName)
return "%s.%s.%s" % (self.__module__, self.__class__.__name__, self._testMethodName)

def id(self): # for XUnit outputs
return self.__str__()

def shortDescription(self): # do not return the docstring
return None

2. For SauceLabs jobs, you can also expose the URL of the job run in which you are running. WebDriverException's inherit from the Exception class, and add a 'msg' property that we can use to insert the SauceLabs URL. You want to avoid adding the URL in the id() and __str__() methods, since those routines are used to dump out the names of classes that Hudson/Jenkins may used to compare against between builds.

def get_sauce_job_url(self):
# Expose SauceLabs job number for easy reference if an error occurs.
if getattr(self, 'webdriver', None) and hasattr(self.webdriver, 'session_id') and self.webdriver.session_id:
session_id = "(" % self.webdriver.session_id
session_id = ''

return session_id

def __str__(self):
session_id = self.get_sauce_job_url()
return " ".join([super(SeleniumTestSuite, self).__str__(), session_id])

def _exc_info(self):
exc_info = super(SeleniumTestSuite, self)._exc_info()

# WebDriver exceptions have a 'msg' attribute, which gets used to be dumped out.
# We can take advantage of this fact and store the SauceLabs jobs URL in there too!
if exc_info[1] and hasattr(exc_info[1], 'msg'):
session_id = self.get_sauce_job_url()
exc_info[1].msg = session_id + "\n" + exc_info[1].msg
return exc_info

3. Nose has a bunch of nifty commands that you should try, including --with-id & --failed, which lets you run your entire test suite and then run only the ones that failed. You can also use the attrib decorator, which lets you to decorate certain test suites/test methods with various attributes, such as network-based tests or slow-running ones. The attrib plugin seems to support a limited boolean logic, so check the documentation carefully if you intend to use the -a flag (you can use --collect-only in conjunction to verify your tests are correctly running with the right logic).

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