feat: Set up comprehensive Python testing infrastructure

[llbbl]

Set up Python Testing Infrastructure

Summary

This PR establishes a complete testing infrastructure for the Python backend using Poetry, pytest, and coverage tools. The setup provides a solid foundation for writing comprehensive unit and integration tests.

Changes Made

Testing Dependencies

• pytest (^8.0.0) - Modern Python testing framework
• pytest-cov (^4.1.0) - Coverage reporting plugin
• pytest-mock (^3.12.0) - Enhanced mocking utilities

Configuration (backend/pyproject.toml)

• pytest configuration: Test discovery patterns, custom markers, strict mode
• coverage configuration: 80% threshold, HTML/XML reports, source inclusion/exclusion
• Poetry scripts: poetry run test and poetry run tests commands

Directory Structure

backend/
├── tests/
│   ├── __init__.py
│   ├── conftest.py          # Shared fixtures
│   ├── unit/__init__.py     # Unit tests
│   ├── integration/__init__.py  # Integration tests
│   └── test_setup_validation.py  # Infrastructure validation

Fixtures and Testing Utilities (tests/conftest.py)

• Temporary file/directory fixtures
• Environment variable mocking
• Mock OpenAI and LangChain clients
• Sample data fixtures for testing
• Agent state mocking for LangGraph tests

Coverage Settings

• Source: app/ directory
• Threshold: 80% minimum coverage
• Reports: Terminal, HTML (htmlcov/), XML (coverage.xml)
• Exclusions: Test files, migrations, standard Python patterns

Running Tests

Basic Commands

# Install dependencies  
poetry install

# Run all tests
poetry run pytest

# Alternative commands
poetry run test
poetry run tests

# Run with specific markers
poetry run pytest -m unit
poetry run pytest -m integration  
poetry run pytest -m slow

Coverage Options

# Run tests with coverage (default)
poetry run pytest

# Coverage reports generated in:
# - Terminal (--cov-report=term-missing)
# - HTML: htmlcov/index.html
# - XML: coverage.xml

Validation

The infrastructure includes validation tests (test_setup_validation.py) that verify:

• ✅ pytest is working correctly
• ✅ Python version compatibility (3.11+)
• ✅ All fixtures are available and functional
• ✅ Custom markers work (unit, integration, slow)
• ✅ App module is importable
• ✅ Mocking capabilities work
• ✅ Coverage configuration is active

All 17 validation tests pass, confirming the infrastructure is ready for use.

Development Workflow

1. Write tests in appropriate directories (tests/unit/ or tests/integration/)
2. Use fixtures from conftest.py for common testing scenarios
3. Run tests with poetry run pytest
4. Check coverage in terminal output or htmlcov/index.html
5. Mark tests with appropriate markers for organization

Notes

• No actual application tests were written - this PR focuses solely on infrastructure
• Poetry lock file is tracked in git as recommended
• .gitignore updated with testing artifacts and Python patterns
• Ready for immediate test development without additional setup

The testing infrastructure provides a professional-grade foundation for maintaining code quality and reliability.