How can i pass objects in metafunc.parametrize

[sar009]

How do I pass objects in pytest_generate_tests > metafunc.parametrize and retain class or session scope. The discussion has been open for quite some time, and I don't have a clear idea on how to fix it. (#5738, #12931).

The code I used to generate is attached below. When I pass a string list in metafunc.parametrize > arg values, the scope is maintained, while when I pass a list of objects, the scope is not maintained. For the code below, I get the following output.

sample.py::TestTestObj::test_some_thing[obj] a--17973f51-280a-4ec2-b8d8-1599fdd41686
sample.py::TestTestObj::test_some_think[obj] a--0055fb8e-7d57-4b21-815e-60a0015c4821
sample.py::TestTestStr::test_some_thing[str] b--0a23f207-1e59-405f-aa6b-f16c22152a4b
sample.py::TestTestStr::test_some_think[str] b--0a23f207-1e59-405f-aa6b-f16c22152a4b

As you see first and second line has different UUIDs (this was the list of objects) while the fixture has class scope, but 3 and 4 have the same UUID(this was the list of strings).

my_class.py

class MyClass:
    def __init__(self, my_param: str):
        self.my_param = my_param

conftest.py

import pytest

from my_class import MyClass


def pytest_generate_tests(metafunc: pytest.Metafunc) -> None:
    if "fixture_obj" in metafunc.fixturenames:
        metafunc.parametrize("fixture_obj", [MyClass("a")], indirect=True, ids=["obj"])
    if "fixture_str" in metafunc.fixturenames:
        metafunc.parametrize("fixture_str", ["b"], indirect=True, ids=["str"])

sample.py

import logging
import uuid
from typing import Any

import pytest

logger = logging.getLogger(__name__)


@pytest.fixture(scope="class")
def fixture_obj(request: Any):
    return f"{request.param.my_param}--{str(uuid.uuid4())}"


@pytest.fixture(scope="class")
def fixture_str(request: Any):
    return f"{request.param}--{str(uuid.uuid4())}"


class TestTestObj:

    def test_some_thing(self, fixture_obj):
        print(fixture_obj)

    def test_some_think(self, fixture_obj):
        print(fixture_obj)


class TestTestStr:

    def test_some_thing(self, fixture_str):
        print(fixture_str)

    def test_some_think(self, fixture_str):
        print(fixture_str)

execute test as

pytest -s --log-cli-level INFO sample.py

[sar009]

def pytest_generate_tests(metafunc: pytest.Metafunc) -> None:
    if "fixture_str" in metafunc.fixturenames:
        values = [str(uuid.uuid4())]
        metafunc.parametrize("fixture_str", values, indirect=True, ids=["str"])

Even fixtures parameterized like these fail! even though it's a list of strings

[sar009]

@RonnyPfannschmidt @nicoddemus Hey folks, sorry to bother you. Wanted some help with this issue if you are aware of it.

[sar009]

What do you mean by passing the matching value? If you don't mind, can you point me to an example or documentation?

[RonnyPfannschmidt]

https://docs.pytest.org/en/latest/reference/reference.html#pytest.Metafunc.parametrize

Not aware of a example right now

[RonnyPfannschmidt]

When using objects its important they are comparable and hashable else each new instance is considered a different parameter variant

[sar009]

Thanks a lot, Ronny, this helped.

class MyClass:
    def __init__(self, my_param: str):
        self.my_param = my_param

    def __eq__(self, other):
        return isinstance(other, MyClass) and self.my_param == other.my_param

    def __hash__(self):
        return hash(self.my_param)

[sar009]

Should I add this notice and the example to the documentation

[RonnyPfannschmidt]

Yes please