unit testing class hierarchies
Terry Reedy
tjreedy at udel.edu
Wed Oct 3 16:14:39 EDT 2012
On 10/3/2012 5:33 AM, Oscar Benjamin wrote:
> On 3 October 2012 02:20, Steven D'Aprano
> <steve+comp.lang.python at 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
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