A session-fixture which can look at all collected tests

A session-scoped fixture effectively has access to all collected test items. Here is an example of a fixture function which walks all collected tests and looks if their test class defines a callme method and calls it:

# content of conftest.py

import pytest

@pytest.fixture(scope="session", autouse=True)
def callattr_ahead_of_alltests(request):
    print("callattr_ahead_of_alltests called")
    seen = set([None])
    session = request.node
    for item in session.items:
        cls = item.getparent(pytest.Class)
        if cls not in seen:
            if hasattr(cls.obj, "callme"):

test classes may now define a callme method which will be called ahead of running any tests:

# content of test_module.py

class TestHello(object):
    def callme(cls):
        print("callme called!")

    def test_method1(self):
        print("test_method1 called")

    def test_method2(self):
        print("test_method1 called")

class TestOther(object):
    def callme(cls):
        print("callme other called")
    def test_other(self):
        print("test other")

# works with unittest as well ...
import unittest

class SomeTest(unittest.TestCase):
    def callme(self):
        print("SomeTest callme called")

    def test_unit1(self):
        print("test_unit1 method called")

If you run this without output capturing:

$ pytest -q -s test_module.py
callattr_ahead_of_alltests called
callme called!
callme other called
SomeTest callme called
test_method1 called
.test_method1 called
.test other
.test_unit1 method called
4 passed in 0.12 seconds