Pytest Backend Testing Guidelines

Purpose

Complete guide for writing comprehensive tests for FastAPI backend applications using pytest, pytest-asyncio, and FastAPI TestClient. Emphasizes async testing, proper mocking, layered testing (repository → service → router), and achieving high test coverage.

When to Use This Skill

• Writing new test files for backend code
• Testing repositories, services, or API routes
• Setting up test fixtures and mocks
• Debugging failing tests
• Improving test coverage
• Writing async tests with pytest-asyncio
• Testing database operations
• Using FastAPI TestClient for route testing