typing.Protocol subclasses are not collected.

• a detailed description of the bug or problem you are having: Extending Protocol and using it with mixin classes won’t collect tests from mixins.
• output of pip list from the virtual environment you are using

attrs     22.1.0 Classes Without Boilerplate
iniconfig 1.1.1  iniconfig: brain-dead simple config-ini parsing
packaging 21.3   Core utilities for Python packages
pluggy    1.0.0  plugin and hook calling mechanisms for python
py        1.11.0 library with cross-python path, ini-parsing, io, code, log facilities
pyparsing 3.0.9  pyparsing module - Classes and methods to define and execute parsing grammars
pytest    7.1.3  pytest: simple powerful testing with Python
tomli     2.0.1  A lil' TOML parser

• pytest and operating system versions:

pytest 7.1.2, ubuntu wayland 22.04, Python 3.10

• minimal example if possible:

File: test_foo.py

from typing import Protocol


class Proto(Protocol):
    a: int = 2
    b: int = 3

    def parse(self) -> int:
        ...


class TestBase(Proto):
    @classmethod
    def add(cls, a, b):
        return a + b

    @classmethod
    def subtract(cls, a, b):
        return a - b


class SubtractTestCase(TestBase):
    def parse(self) -> int:
        return self.subtract(self.a, self.b)


class AddTestCase(TestBase):
    def parse(self) -> int:
        return self.add(self.a, self.b)


class OneTestMixin(Proto):
    a = 3
    b = 3

    def test_parse(self):
        assert self.parse() in (0, 6)


class TestOneAdd(AddTestCase, OneTestMixin):
    ...

class TestOneSubstract(SubtractTestCase, OneTestMixin):
    ...

run py.test no test would be collected. If you would omit Protocol from Proto everything will pass.

repo with the code: https://github.com/nrbnlulu/pytest-protocol-issue

[RonnyPfannschmidt]

The benefit of protocol typically is that you intentionally do not have it on the implementation classes

[nrbnlulu]

Yeah, I just realized this.