swev-id: pytest-dev__pytest-6197 Fix: avoid importing non-test __init__.py during collection; restore 5.2.2 behavior

[casey-brooks]

Summary

• prevent package collectors from importing __init__.py unless the file matches python_files or was explicitly requested
• keep package-level setup/teardown hooks guarded behind the same check to avoid importing non-test packages during setup
• add regression coverage for default, python_files opt-in, src/ layout, and namespace packages

Testing

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest testing/python/collect.py -k "package_init_not_imported_when_not_a_test_module or package_init_collected_when_enabled_via_python_files or src_layout_package_init_not_imported or namespace_package_without_init_collects_normally" -q
• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest testing/test_collection.py -q

Fixes #19

Root cause

Package.collect unconditionally imported the package via _mount_obj_if_needed(), which executes __init__.py even when the file is not considered a test module. This regressed after the package-scoped fixture work in 5.2.3.

Fix details

• introduce _should_import_init() to decide when __init__.py should be mounted/collected (matches python_files or the file was explicitly targeted)
• guard both collect() and setup() behind this check so that boundary-level hooks remain intact without importing non-test packages prematurely
• adjust collection tests to reflect the explicit-selection behavior and cover the regression scenarios (default layout, python_files opt-in, src layout, namespace package)

Reproduction steps and observed failure

1. Create pkg/__init__.py with assert False and place unrelated tests elsewhere (e.g. tests/test_ok.py).
2. Run pytest from the project root under 5.2.3.
3. Collection fails with AssertionError while importing pkg/__init__.py even though it is not a test module.

Compatibility

• python_files opt-in still collects package __init__.py containing tests.
• namespace packages (no __init__.py) remain unaffected.
• src/ layouts avoid importing application packages during discovery.
• explicit selection (pytest pkg/__init__.py) continues to work via the initialpaths guard.

[casey-brooks]

Local Verification

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest testing/python/collect.py -k "package_init_not_imported_when_not_a_test_module or package_init_collected_when_enabled_via_python_files or src_layout_package_init_not_imported or namespace_package_without_init_collects_normally" -q
  • Result: 4 passed (74 deselected)
• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest testing/test_collection.py -q
  • Result: 71 passed, 1 xfailed
• .venv/bin/flake8 src/_pytest/python.py testing/python/collect.py testing/test_collection.py
  • Result: no issues

[noa-lucent]

Changes look good: guarding package init import behind python_files/explicit selection restores expected behavior, and regression tests cover the updated scenarios.