Python Testing Patterns

Iron Law

NO TEST INFRASTRUCTURE WITHOUT READING THE PLAYBOOK FIRST — fixtures, markers, and coverage config have workspace-specific patterns that prevent test debt

Python Testing Patterns

Deep reference for pytest test infrastructure, fixtures, async patterns, and CI integration for Python 3.14 / FastAPI services.

When to Use

Load this skill when:

• Setting up a new test suite from scratch (conftest.py, pyproject.toml config)
• Writing parametrized tests for multiple input scenarios
• Mocking async dependencies (AsyncMock patterns)
• Testing database operations with session fixtures
• Configuring test markers (slow, integration) for selective execution
• Setting up coverage reporting gates
• Wiring GitHub Actions CI for Python tests

Load test-driven-development skill first for the Red-Green-Refactor process. This skill handles the infrastructure — not the TDD process.

Quick Reference

Reference File

Load resources/implementation-playbook.md for:

• 10 fundamental patterns (fixtures, parametrize, mocking, async, monkeypatch, tmp_path, Hypothesis)
• 10 advanced patterns (DB fixtures, test markers, coverage config, CI workflow, test organization)
• Full conftest.py templates
• GitHub Actions workflow for Python tests
• pytest.ini / pyproject.toml configuration

Relationship to Other Skills

• test-driven-development — process (Red-Green-Refactor, when to write tests, naming)
• python-testing-patterns — infrastructure (how to structure, configure, and run tests)
• agentic-ai-dev/reference/agentic-testing.md — LangGraph agent-specific testing patterns

Post-Test Checklist

• pytest -q — all tests pass
• pytest --cov=src --cov-report=term-missing — coverage visible
• No print() in test files — use capfd fixture or logging
• Async tests use @pytest.mark.asyncio or asyncio_mode = "auto" in config
• External services mocked — no real HTTP calls in unit tests