Halting Python unittest Execution on First Error

We all know the importance of unit tests. Especially in a dynamic language like Python. Occasionally you have a set of unit tests that are failing in a cascading fashion where the first error case causes subsequent tests to fail (these tests are likely no longer unit tests, but that’s a different discussion). To help isolate the offending test case in a see of failures you can set the unittest.TestCase class to halt after the first error by overriding the run method as follows.

class HaltingTestCase(unittest.TestCase):

    def run(self, result=None):
        """ Stop after first error """
        if not result.errors:
            super(HaltingTestCase, self).run(result)

In this block of code, if we do not have any errors we call the super class to continue running tests. If we have an error execution stops after this method call. This allows you to pinpoint the first error case, fix it, and continue on fixing subsequent tests.