Python unittest - setUpClass() is giving me trouble - why can't I inherit like this?

Question

I have unittest code like the following:

import unittest  class MyUnitTest(unittest.TestCase):     def setUpClass(self):         do_something_expensive_for_all_sets_of_tests()  class MyFirstSetOfTests(MyUnitTest):     def setUpClass(self):         super(MyFirstSetOfTests, self).setUpClass()         do_something_expensive_for_just_these_first_tests()      def test_one(self):         ...      def test_two(self):         ...  class MySecondSetOfTests(MyUnitTest):     def setUpClass(self):         super(MySecondSetOfTests, self).setUpClass()         do_something_expensive_for_just_these_second_tests()      def test_one(self):         ...      def test_two(self):         ...  if __name__ == '__main__':     unittest.main() 

When I try to run this code, I get an error like this:

====================================================================== ERROR: setUpClass (__main__.MyFirstSetOfTests) ---------------------------------------------------------------------- TypeError: unbound method setUpClass() must be called with MyFirstSetOfTests instance as first argument (got nothing instead)  ---------------------------------------------------------------------- 

Answer 1

setUpClass must be a class method. From the documentation:

A class method called before tests in an individual class run. setUpClass is called with the class as the only argument and must be decorated as a classmethod():

@classmethod def setUpClass(cls):     ... 

See Class and Module Fixtures for more details.

Your version is missing the @classmethod decorator:

class MyUnitTest(unittest.TestCase):     @classmethod     def setUpClass(cls):         do_something_expensive_for_all_sets_of_tests()  class MyFirstSetOfTests(MyUnitTest):     @classmethod     def setUpClass(cls):         super(MyFirstSetOfTests, cls).setUpClass()         do_something_expensive_for_just_these_first_tests() 

The error is thrown because MyFirstSetOfTests.setUpClass() is called on the class, not on an instance, but you didn't mark your method as a classmethod and thus it was not passed in the automatic self argument. In the above updated code I used cls instead, to reflect that the name references the class object.