How to run the same test-case for different classes?

Question

I have several classes that share some invariants and have a common interface, and I would like to run automatically the same test for each of them.

As an example, suppose I have several classes that implement different approaches for partitioning a data-set. The common invariant here would be, that for all of these classes the union over all partitions should equal the original data-set.

What I currently have looks something like this:

class PartitionerInvariantsTests(unittest.TestCase):
    def setUp(self):
        self.testDataSet = range(100) # create test-data-set

    def impl(self, partitioner):
        self.assertEqual(self.testDataSet, 
                         chain.from_iterable(partitioner(self.testDataSet))

Then I add a different function that calls impl for each of the classes I want to test with an instance of that class. The problem with this becomes apparent when doing this for more than one test-function. Suppose I have 5 test-functions and 5 classes I want to test. This would make 25 functions that look almost identical for invoking all the tests.

Another approach I was thinking about was to implement the template as a super-class, and then create a sub-class for each of the classes I want to test. The sub-classes could provide a function for instantiating the class. The problem with that is that the default test-loader would consider the (unusable) base-class a valid test-case and try to run it, which would fail.

So, what are your suggestions?

P.S.: I am using Python 2.6

Answer 1

You could use multiple inheritance.

class PartitionerInvariantsFixture(object):
    def setUp(self):
        self.testDataSet = range(100) # create test-data-set
        super(PartitionInvariantsFixture, self).setUp()

    def test_partitioner(self):
        TestCase.assertEqual(self.testDataSet, 
                     chain.from_iterable(self.partitioner(self.testDataSet))

class MyClassTests(TestCase, PartitionerInvariantsFixture):
    partitioner = Partitioner