• Include a detailed description of the bug or suggestion

With pytest 4.2.0, there is a change of behaviour regarding unittest classes using unittest.skip decorator. Classes that were completely skipped before now run inherited setUpClass before skipping the test class.
This only happens with inherited setUpClass, not with setUpClass defined directly in the test class.

• pip list of the virtual environment you are using

Package        Version
-------------- -------
atomicwrites   1.2.1
attrs          18.2.0
more-itertools 5.0.0
pathlib2       2.3.3
pip            19.0.1
pluggy         0.8.1
py             1.7.0
pytest         4.2.0
setuptools     40.7.1
six            1.12.0
wheel          0.32.3

• pytest and operating system versions
  platform linux -- Python 3.5.3, pytest-4.2.0, py-1.7.0, pluggy-0.8.1
• Minimal example if possible
  This example test is skipped with pytest 4.1.1 and raises an error with pytest 4.2.0:

import unittest


class ClassPrinter(unittest.TestCase):

    @classmethod
    def setUpClass(cls):
        print(cls.name)


@unittest.skip('this class fails')
class TestClassFailed(ClassPrinter):

    name = 'failure'

    def test_failure(self):
        raise Exception('this test fails')