python-testing

Python testing patterns with pytest, fixtures, TDD, mocking, async and integration tests

Night Market Skill — ported from claude-night-market/parseltongue. For the full experience with agents, hooks, and commands, install the Claude Code plugin.

Python Testing Hub

Testing standards for pytest configuration, fixture management, and TDD implementation.

Table of Contents

1. Quick Start
2. When to Use
3. Modules

Quick Start

1. Dependencies: pip install pytest pytest-cov pytest-asyncio pytest-mock
2. Configuration: Add the following to pyproject.toml:

   toml

   [tool.pytest.ini_options]
   testpaths = ["tests"]
   addopts = "--cov=src"
   

3. Verification: Run pytest to confirm discovery of files matching test_*.py.

When To Use

• Constructing unit and integration tests for Python 3.9+ projects.
• Isolating external dependencies using pytest-mock or custom monkeypatching.
• Validating asynchronous logic with pytest-asyncio markers and event loop management.
• Configuring project-wide coverage thresholds and reporting.

When NOT To Use

• Evaluating test quality - use pensive:test-review instead
• Infrastructure test config - use leyline:pytest-config

Modules

This skill uses modular loading to manage the system prompt budget.

Core Implementation

• See modules/unit-testing.md - AAA (Arrange-Act-Assert) pattern, basic test structure, and exception validation.
• See modules/fixtures-and-mocking.md - Request-scoped fixtures, parameterization, and boundary mocking.
• See modules/async-testing.md - Coroutine testing, async fixtures, and concurrency validation.

Infrastructure & Workflow

• See modules/test-infrastructure.md - Directory standards, conftest.py management, and coverage tools.
• See modules/testing-workflows.md - Local execution patterns and GitHub Actions integration.

Standards

• See modules/test-quality.md - Identification of common anti-patterns like broad exception catching or shared state between tests.

Exit Criteria

• Tests implement the AAA pattern.
• Coverage reaches the 80% project minimum.
• Individual tests are independent and do not rely on execution order.
• Fixtures are scoped appropriately (function, class, or session) to prevent side effects.
• Mocking is restricted to external system boundaries.

Troubleshooting

• Test Discovery: Verify filenames match the test_*.py pattern. Use pytest --collect-only to debug discovery paths.
• Import Errors: Ensure the local source directory is in the path, typically by installing in editable mode with pip install -e ..
• Async Failures: Confirm that pytest-asyncio is installed and that async tests use the @pytest.mark.asyncio decorator or corresponding auto-mode configuration.