Path: csiph.com!newsfeed.hal-mli.net!feeder3.hal-mli.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!newsfeed.xs4all.nl!newsfeed5.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: unit testing class hierarchies
Date: Wed, 03 Oct 2012 16:14:39 -0400
References: <v53rj9-5kd.ln1@satorlaser.homedns.org> <mailman.1725.1349186875.27098.python-list@python.org> <irirj9-sme.ln1@satorlaser.homedns.org> <mailman.1748.1349217065.27098.python-list@python.org> <506b92f3$0$29982$c3e8da3$5496439d@news.astraweb.com> <CAHVvXxQN1B0iZHVSQGh0++f=G_g=bpi0a+QZYznrcjaVSQwUzA@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:15.0) Gecko/20120824 Thunderbird/15.0
In-Reply-To: <CAHVvXxQN1B0iZHVSQGh0++f=G_g=bpi0a+QZYznrcjaVSQwUzA@mail.gmail.com>
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.1831.1349402456.27098.python-list@python.org>
Lines: 63
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:30772

On 10/3/2012 5:33 AM, Oscar Benjamin wrote:
> On 3 October 2012 02:20, Steven D'Aprano
> <steve+comp.lang.python@pearwood.info> wrote:
>>
>> But surely, regardless of where that functionality is defined, you still
>> need to test that both D1 and D2 exhibit the correct behaviour? Otherwise
>> D2 (say) may break that functionality and your tests won't notice.
>>
>> Given a class hierarchy like this:
>>
>> class AbstractBaseClass:
>>      spam = "spam"
>>
>> class D1(AbstractBaseClass): pass
>> class D2(D1): pass
>>
>>
>> I write tests like this:
>>
>> class TestD1CommonBehaviour(unittest.TestCase):
>>      cls = D1
>>      def testSpam(self):
>>           self.assertTrue(self.cls.spam == "spam")
>>      def testHam(self):
>>           self.assertFalse(hasattr(self.cls, 'ham'))
>>
>> class TestD2CommonBehaviour(TestD1CommonBehaviour):
>>      cls = D2
>
> That's an excellent idea. I wanted a convenient way to run the same
> tests on two classes in order to test both a pure python and a
> cython-accelerator module implementation of the same class.

Python itself has same issue with testing Python and C coded modules. It 
has the additional issue that the Python class by default import the C 
version, so additional work is needed to avoid that and actually test 
the python code.

For instance, heapq.test_heapq.py has

...
py_heapq = support.import_fresh_module('heapq', blocked=['_heapq'])
c_heapq = support.import_fresh_module('heapq', fresh=['_heapq'])
...
class TestHeap(TestCase):
     module = None
... <multiple test methods for functions module.xxx>

class TestHeapPython(TestHeap):
     module = py_heapq

@skipUnless(c_heapq, 'requires _heapq')
class TestHeapC(TestHeap):
     module = c_heapq
...
def test_main(verbose=None):
     test_classes = [TestModules, TestHeapPython, TestHeapC,

# TestHeap is omitted from the list and not run directly

-- 
Terry Jan Reedy