Python Testing Skill for Claude

Python Testing Hub

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

Table of Contents

• Quick Start
• When to Use
• Modules

Quick Start

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

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

• 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.