Coverage misses import-time lines: run pytest under coverage instead of pytest-cov

[CaptainDriftwood]

Problem

Coverage numbers are systematically deflated and three modules are excluded outright. Root cause: the icap package registers a pytest11 entry-point plugin, so pytest imports the whole package during plugin loading, before pytest-cov starts measuring. Every module-level line (imports, def/class statements, decorators, constants) is recorded as missed, and the config works around it by omitting __init__.py, exception.py, and _protocol.py ('executed before coverage starts').

The _protocol.py omit is now costly: since the shared-logic refactor it contains core parsing/validation (parse_chunk_size, parse_response_headers, _validate_service_name, prepare_preview_data) with zero coverage visibility.

Validated fix

Run pytest under coverage so measurement starts at interpreter level, before plugin loading:

coverage run -m pytest -m 'not integration'
coverage combine
coverage report / coverage xml

Measured on the same test run (unit tests only), before → after:

Module	pytest-cov	coverage run
icap.py	85%	92%
response.py	61%	93%
__init__.py	omitted	100%
exception.py	omitted	100%
_protocol.py	omitted	98%

Remaining missing lines after the switch are genuine behavioral gaps (tracked separately), not import-time noise.

Changes

• noxfile.py coverage sessions: replace pytest --cov=src/icap with coverage run -m pytest + coverage combine + coverage report --show-missing + coverage xml (config already has parallel = true); drop the pytest-cov dep from those sessions.
• Remove the omit entries for __init__.py, exception.py, _protocol.py in pyproject.toml.
• If coverage runs ever adopt xdist (-n auto): add patch = ["subprocess"] to [tool.coverage.run] (requires coverage >= 7.10; lockfile has 7.13.4) so worker processes are measured from interpreter startup too.
• Consider setting fail_under (~85%) once the numbers are trustworthy.
• Update the CI coverage job if it invokes pytest-cov directly.