# content of conftest.py or a tests file (e.g. in your tests or root directory)

@pytest.fixture(scope="session", autouse=True)
def do_something(request):
    # prepare something ahead of all tests
    request.addfinalizer(finalizer_function)

# content of conftest.py

def pytest_sessionstart(session):
    """ before session.main() is called. """
    pass

def pytest_sessionfinish(session, exitstatus):
    """ whole test run finishes. """
    pass

setUpClass()

A class method called before tests in an individual class run

tearDownClass()

A class method called after tests in an individual class have run.