Fix pytest CI matrix compatibility and prevent hangs

[Copilot]

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.

[Copilot]

Pull request overview

This PR updates the Python test/CI setup so the GitHub Actions matrix actually runs the intended pytest versions (stable wildcard + pre-release), removes an obsolete pytest pin caused by pytest-black, and hardens the pytestadapter test harness to avoid indefinite hangs when subprocess/pipe communication fails.

Changes:

• Reorders/install-adjusts pytest in CI workflows and removes the global pytest<8.1 / pytest-black constraints that were downgrading matrix-selected pytest.
• Adds bounded waits/timeouts and clearer failure propagation in python_files/tests/pytestadapter/helpers.py to prevent CI hangs.
• Adds regression tests for subprocess timeout, pipe timeout, and failure surfacing; introduces a local replacement conftest for the black-related test data.

Show a summary per file

File	Description
python_files/tests/pytestadapter/test_helpers.py	Adds regression tests covering subprocess timeout and pipe/failure handling.
python_files/tests/pytestadapter/test_coverage.py	Switches to PYTEST_DISABLE_PLUGIN_AUTOLOAD env var for cross-version compatibility.
python_files/tests/pytestadapter/helpers.py	Adds subprocess timeout and bounded pipe waits; refactors runner to avoid hang scenarios.
python_files/tests/pytestadapter/.data/2496-black-formatter/conftest.py	Provides a local, pytest-8.4+ compatible black-check collector for test data.
build/test-requirements.txt	Removes pytest<8.1 and pytest-black from shared test requirements.
.github/workflows/pr-check.yml	Expands Python versions and installs matrix-selected pytest after test requirements.
.github/workflows/build.yml	Ensures pytest is explicitly installed in the build workflow.

Review details

• Files reviewed: 7/7 changed files
• Comments generated: 1
• Review effort level: Low