Sometimes, when writing tests in Pytest, I find myself using fixtures that the test
function/method doesn’t directly reference. Instead, Pytest runs the fixture, and the test
function implicitly leverages its side effects. For example:
import os
from collections.abc import Iterator
from unittest.mock import Mock, patch
import pytest
# Define an implicit environment mock fixture that patches os.environ
@pytest.fixture
def mock_env() -> Iterator[None]:
with patch.dict("os.environ", {"IMPLICIT_KEY": "IMPLICIT_VALUE"}):
yield
# Define an explicit service mock fixture
@pytest.fixture
def mock_svc() -> Mock:
service = Mock()
service.process.return_value = "Explicit Mocked Response"
return service
# IDEs tend to dim out unused parameters like mock_env
def test_stuff(mock_svc: Mock, mock_env: Mock) -> None:
# Use the explicit mock
response = mock_svc.process()
assert response == "Explicit Mocked Response"
mock_svc.process.assert_called_once()
# Assert the environment variable patched by mock_env
assert os.environ["IMPLICIT_KEY"] == "IMPLICIT_VALUE"
In the test_stuff function above, we directly use the mock_svc fixture but not
mock_env. Instead, we expect Pytest to run mock_env, which modifies the environment
variables. This works, but IDEs often mark mock_env as an unused parameter and dims it
out.