Test isolation and tiers

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:

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.