cuioss/pytest-testing

Pytest Testing Standards

REFERENCE MODE: This skill provides reference material for writing pytest tests. Load standards on-demand based on current task.

Enforcement

Execution mode: Reference library; load standards on-demand for Python testing tasks.

Prohibited actions:

• Do not use unittest.TestCase for new tests; use plain pytest functions
• Do not share mutable state between tests without fixture isolation
• Do not use os.chdir() without restoration (use monkeypatch.chdir())

Constraints:

• Tests must follow AAA (Arrange-Act-Assert) pattern
• Each test must be independent and isolated
• Fixtures must use appropriate scope (function/module/session)
• Working directory changes must be restored after each test

When to Use This Skill

Activate when:

• Writing new pytest tests — test structure, naming, AAA pattern
• Debugging test failures — isolation issues, fixture scoping, state leaks
• Adding fixtures — shared setup, parametrization, conftest organization
• Mocking dependencies — monkeypatch, unittest.mock.patch, state patching
• Reviewing test code — checking isolation, assertion quality, coverage gaps
• Configuring test infrastructure — conftest.py, markers, coverage settings

Available References

File: standards/testing-pytest.md (331 lines)

Load When:

• Writing or reviewing pytest test code
• Setting up test infrastructure (conftest, fixtures)
• Debugging isolation or mocking issues
• Organizing test file structure

Contents:

• Test naming conventions (files and functions)
• AAA pattern with examples
• Isolation patterns (tmp_path, monkeypatch, _restore_cwd)
• Script path discovery (dual-path pattern)
• Fixture scope and autouse
• Parametrization
• Property-based and adversarial testing (Hypothesis)
• Mocking (module state, functions)
• Assertions (basic, exceptions, approximate)
• Output capture (capsys, capfd)
• Subprocess / script testing patterns (structured output, PYTHONPATH, error paths)
• Event-loop and wall-clock CI liabilities (asyncio.run loop-close hangs, calendar time-bombs, pytest-timeout backstop)
• Test organization (conftest, file structure)

Load Command:

Read standards/testing-pytest.md

Quick Reference

| Topic | Rule | |-------|------| | File naming | test_<module>.py | | Function naming | test_<behavior> — descriptive of what is tested | | Structure | Arrange-Act-Assert (AAA) | | Isolation | tmp_path for files, monkeypatch for state, autouse _restore_cwd | | Fixtures | conftest.py for shared, function scope by default | | Parametrize | @pytest.mark.parametrize for input variations | | Property-based / adversarial | Hypothesis @given / strategies / @example (third-party hypothesis dep — user-approval) | | Exceptions | pytest.raises(ExcType, match="pattern") | | Approximate | pytest.approx(value, rel=tolerance) | | Output capture | capsys for Python, capfd for subprocess output | | Script testing | subprocess.run with capture_output=True, text=True, timeout=30 |

Running Tests

# Via build system
python3 .plan/execute-script.py plan-marshall:build-pyproject:pyproject_build run --command-args "module-tests"

# Specific module
python3 .plan/execute-script.py plan-marshall:build-pyproject:pyproject_build run --command-args "module-tests pm-dev-python"

# With coverage
python3 .plan/execute-script.py plan-marshall:build-pyproject:pyproject_build run --command-args "coverage"

Related Skills

• pm-dev-python:python-core - Core Python development patterns
• plan-marshall:persona-module-tester - Language-agnostic testing methodology