When I use a patch wrapper in test, PTO19 fires when the patched items passed into the argument are unused

[jplhanna]

Bug report

What's wrong

I use the unit test patch as a wrapper around test cases and test functions, which requires the patched items to be passed into the test as the first X arguments.
The name of the arguments doesn't matter, they are just passed in reverse order of the patches.

When running flake8 against a test file with such a use case and the argument is not used, PT019 will fire saying the fixture without value should be placed in pytest.mark.usefixtures.

Example:

@patch.object(Config, "get_first", return_value=None)
@patch("src.app.config.controllers.db")
class TestCreateConfigFromExisting:
    def test_new_config_has_given_unit(self, _mock_db, _get_config):
        # Arrange
        mock_unit = MagicMock()
        existing_config = Config(categories=[])

        # Act
        config = create_item_from_existing(mock_unit, existing_config)

        # Assert
        assert config.unit == mock_unit

_mock_db and _get_config will fire PT019

How it should work

I would expect this case to be ignored, or suggest placing _ in front of the argument if the patched item is not used in the test.

System information

• Operating system: MacOS Monterey
• Python version: 3.8
• flake8 version: 4.0.1
• flake8-pytest-style version: 1.6.0

[m-burst]

Hi @jplhanna,
Thanks for the report!
I have not considered this case when writing the rule.

I am not sure when I can find the time to look into a proper fix.
However, I might suggest a workaround using the mocker fixture from the pytest-mock library, so your test would look like this:

@pytest.fixture()
def _mock_get_config(mocker):
    mocker.patch.object(Config, "get_first", return_value=None)

@pytest.fixture()
def _mock_db(mocker):
    mocker.patch("src.app.config.controllers.db")

@pytest.mark.usefixtures("_mock_get_config", "_mock_db")
class TestCreateConfigFromExisting:
    def test_new_config_has_given_unit(self):
        # Arrange
        mock_unit = MagicMock()
        existing_config = Config(categories=[])

        # Act
        config = create_item_from_existing(mock_unit, existing_config)

        # Assert
        assert config.unit == mock_unit

[jplhanna]

Thanks for the suggestion! It might be tough to use for the current project but I'll keep it in mind for future ones.
I figured this wouldn't be an easy/quick fix. Just something worth noting.

[funkyfuture]

when the name _in (as complement to out) is used with parametrized tests it also evokes false PT019. or any other name starting with _.

[m-burst]

I would suggest using in_ instead of _in, because a leading underscore conventionally implies that the name is unused