# Red fixture for Python unit isolation, external deps (#121, slice 3). A unit test
# must mock external collaborators too — a third-party package and effectful stdlib
# imported and used for real are violations; pure stdlib is fine.
# unit under test — never a collaborator
# third-party — NOT mocked → violation
# effectful stdlib (subprocess) — NOT mocked → violation
# pure stdlib — fine, never a collaborator
# Uses the real collaborators — not isolated.
assert is not None