Question

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How do you generate dynamic (parameterized) unit tests in Python?

Is there a way to dynamically create unittest test cases? I have tried the following…

class test_filenames(unittest.TestCase):

    def setUp(self):
        for category, testcases in files.items():
            for testindex, curtest in enumerate(testcases):
                def thetest():
                    parser = FileParser(curtest['input'])
                    theep = parser.parse()
                    self.assertEquals(theep.episodenumber, curtest['episodenumber'])

                setattr(self, 'test_%s_%02d' % (category, testindex), thetest)

..which creates all the methods correctly (they show up in dir() and are callable), but unittest’s test detector, nor nosetest executes them ("Ran 0 tests in …")

Since I may be asking the wrong question – what I am trying to achieve:

I have a file containing test data, a list of input filenames, and expected data (simplified to episodenumber in the above code), stored in a Python dictionary. The key is the category, the value is a list of test cases, for example…

test_cases = {}
test_cases['example_1'] = [
    {'input': 'test.01',
    'episodenumber': 1},
    {'input': 'test.02',
    'episodenumber': 2}
]

test_cases['example_2'] = [
    {'input': 'another.123',
    'episodenumber': 123},
    {'input': 'test.e42',
    'episodenumber': 32}
]

Currently I just loop over all the data, call self.assertEquals on each test. The problem is, if one fails, I don’t see the rest of the failures as they are also grouped into one test, which aborts when an assertion fails.

The way around this, I thought, would be to (dynamically) create a function for each test case, perhaps there is a better way?

Answer 1

For this you should use test generators in nose. All you need to do is yield a tuple, with the first being a function and the rest being the args. From the docs here is the example.

def test_evens():
    for i in range(0, 5):
        yield check_even, i, i*3

def check_even(n, nn):
    assert n % 2 == 0 or nn % 2 == 0