When adding or changing behavior, require unit tests that are (a) comprehensive for the logic contract, (b) correctly prioritized/selected via pytest markers, and (c) isolated from global state to avoid cross-suite flakiness. Apply it like this: - Cover the real decision points and fallbacks: defaults, manual-vs-auto modes, empty inputs, type/probe fallbacks, and output shape/values. - Use the right pytest marker level so the test actually runs in your expected pipeline (e.g., don’t leave important coverage at `p3` if it won’t execute by default). Ensure markers are registered in `pyproject.toml`. - If tests stub imports or mutate `sys.modules`/env, isolate that mutation with `autouse` fixtures that restore the original state after each test. Example pattern for isolating `sys.modules` stubs: ```python import sys import pytest from types import ModuleType @pytest.fixture(autouse=True) def isolate_sys_modules(): original = sys.modules.copy() try: yield finally: sys.modules.clear() sys.modules.update(original) def test_something_with_stubbed_google_lib(): sys.modules["googleapiclient"] = ModuleType("googleapiclient") # ... import/use code under test safely ... ``` Additionally, for refactors that change call paths, either rely on the expanded unit tests above or attach lightweight scenario-based verification to show behavior is unchanged.