Summary

Fix the Python test matrix so every job runs its requested pytest version, cover supported Python versions against recent and upcoming pytest releases, remove the obsolete global pytest pin, and prevent subprocess failures from hanging CI indefinitely.

Root cause

pytest-black==0.6.0 uses the deprecated pytest_collect_file(path, ...) hook removed by pytest 8.1. The resulting pytest<8.1 workaround lived in shared test requirements, which were installed after the matrix-selected pytest version and silently downgraded stable and pre-release jobs to pytest 8.0.2.

The downgrade also made the manual pytest-cov test reject --disable-plugin-autoload. Its subprocess exited, but the named-pipe listener waited indefinitely, causing the multi-hour CI hangs.

Test matrix

On Ubuntu and Windows:

• Python 3.10, 3.11, 3.12, 3.13, and 3.14
• Latest pytest 8.4 patch (pytest==8.4.*) for approximately one year of compatibility coverage
• Pytest pre-release channel to catch upcoming breaking changes

This produces 20 jobs. The 8.4 wildcard currently resolves to pytest 8.4.2.

Changes

• Install shared test requirements before matrix-selected pytest.
• Remove pytest<8.1 and pytest-black from shared requirements.
• Skip the obsolete pytest-black-specific discovery case; pytest-ruff continues to cover plugin-generated test items.
• Explicitly install stable pytest in the build workflow.
• Use PYTEST_DISABLE_PLUGIN_AUTOLOAD for cross-version manual plugin loading.
• Bound subprocess and pipe waits and propagate failures promptly.
• Add regression tests for subprocess timeout, failure propagation, and pipe timeout.

Validation

• Python 3.10 / pytest 8.4.2: 219 passed, 1 skipped
• Python 3.13 / pytest 9.1.1: 219 passed, 1 skipped
• Ruff checks and git diff --check pass.