Unittest multiple subclasses

Question

I have a code structure where we have a lot of sub classes from a common base class.
I want in an automated fashion test each subclass without having a separate class definition inheriting from TestCase for each subclass.

with a classs like

class MyBaseClass:
    ...

I can get a list of all subclasses that inherits from MyBaseClass with

import all_module_that_includes_subclasses

list_of_all_subclasses = MyBaseClass.__subclasses__()

But how do I connect to this list of scubclasses to avoid manually createing TestCases for each subclass like:

class TestSubClass1(TestCase):
   def test_method_1(self):
      ...
   ...

class TestSubClass2(TestCase):
   def test_method_1(self):
      ...
   ...

etc.

I thought of setting up an instance of all classes in setUp() method and looping through them in each def test_method_#(). This will somewhat work, I think, but it will break as soon as one single class fails. I want to be able to run through all classes and get a full report what class failed and in what tests.

Thankful for help :)

a_guest · Accepted Answer · 2021-04-21 13:49:07Z

1

You can create those test cases dynamically using the load_tests protocol. For this you simply define a top-level function called load_tests which should return a TestSuite.

import unittest


class MyBaseClass:
    pass


class Foo(MyBaseClass):
    pass


class Bar(MyBaseClass):
    pass


class TestBases:
    # Wrapped into other class, so it won't be discovered by unittest.
    class TestCase(unittest.TestCase):
        subclass: MyBaseClass

        def test(self):
            self.assertIsInstance(self.subclass(), MyBaseClass)


def load_tests(loader, tests, pattern):
    for cls in MyBaseClass.__subclasses__():
        test_cls = type(f'Test{cls.__name__}', (TestBases.TestCase,), dict(subclass=cls))
        tests.addTests(loader.loadTestsFromTestCase(test_cls))
    return tests


if __name__ == '__main__':
    unittest.main()

This runs the two dynamically generated test cases TestFoo and TestBar:

$ python /tmp/test.py -v
test (__main__.TestFoo) ... ok
test (__main__.TestBar) ... ok

----------------------------------------------------------------------
Ran 2 tests in 0.000s

answered Apr 21, 2021 at 13:49

a_guest

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1 Comment

Magnus Sommarsjö Over a year ago

Thanks @a_guest, This helped me a lot and I got it working. Some key things here that you wrote is actually the type( ... ) command which dynamically creates the TestCases with correct subclass attached. Ref The way that you are using a wrapper and a base test class is a nice way as well. Thank you a lot!

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