fix: enable strict positional enforcement for the test suite under pytest

[skippdot]

Fixes #2755

The test suite is written against strict positional parameter enforcement (TypeError on violation), but that mode was only ever switched on inside the nose-era setup_package() hook in tests/__init__.py — a hook pytest never calls. Under pytest the suite silently runs in the default warning-only mode.

The reason full runs still pass is an accident of ordering, which is the second half of the problem: the PositionalTests methods in tests/test__helpers.py mutate the module-level positional_parameters_enforcement flag and never restore it. Alphabetical execution leaves test_usage (which sets EXCEPTION) as the last write, so tests/test_discovery.py happens to run strict. Any other order breaks it — reproducible on an unmodified main:

pytest "tests/test__helpers.py::PositionalTests::test_enforcement_ignore" \
       "tests/test_discovery.py::DiscoveryErrors::test_tests_should_be_run_with_strict_positional_enforcement"
# → 1 failed (AssertionError: should have raised a TypeError exception over missing http=.)

as is running tests/test_discovery.py on its own.

Changes

• tests/__init__.py: set positional_parameters_enforcement = util.POSITIONAL_EXCEPTION at import time (using the constant rather than the raw string) and delete the dead setup_package() hook — nothing references it.
• tests/test__helpers.py: add setUp/tearDown to PositionalTests to save and restore the enforcement flag, so these tests stop leaking global state into the rest of the suite.

Two files, +13/−4.

Verification (Python 3.14)

Scenario	before	after
strict test in isolation	failed	passed
test_enforcement_ignore ordered before the strict test	failed	2 passed
tests/test_discovery.py alone	1 failed, 172 passed	173 passed
full tests/ folder	passed by luck	338 passed, 1 skipped
reversed file order (test_discovery.py before test__helpers.py)	order-dependent	183 passed

black --check clean; flake8 --select=E9,F63,F7,F82 (the set CI enforces) clean.

[gemini-code-assist]

Code Review

This pull request updates the test suite initialization to set positional parameter enforcement at import time, ensuring compatibility with pytest, and adds state restoration to PositionalTests to prevent side effects. The reviewer suggests using self.addCleanup in setUp as a more robust and idiomatic way to restore the module-level enforcement setting instead of using a separate tearDown method.