feat: Set up comprehensive Python testing infrastructure

[llbbl]

Add Complete Python Testing Infrastructure

Summary

This PR establishes a comprehensive testing infrastructure for the Streamlit auto-filter dataframe project using Poetry as the package manager and pytest as the testing framework.

Changes Made

Package Management

• Poetry Configuration: Set up pyproject.toml with Poetry as package manager
• Dependencies: Migrated existing dependencies (streamlit, pandas) and added testing dependencies
• Python Version: Configured proper Python version constraints (>=3.9, !=3.9.7, <4.0) for Streamlit compatibility

Testing Dependencies Added

• pytest ^7.4.0 - Main testing framework
• pytest-cov ^4.1.0 - Coverage reporting
• pytest-mock ^3.11.0 - Mocking utilities

Testing Configuration

• pytest settings: Configured in pyproject.toml with test discovery patterns, coverage settings, and custom markers
• Coverage: 80% threshold, HTML/XML/terminal reporting, proper source/exclusion paths
• Markers: Added unit, integration, and slow test markers for test categorization

Directory Structure

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

Fixtures and Test Utilities

Created comprehensive conftest.py with fixtures for:

• DataFrame fixtures: sample, empty, numeric, categorical, datetime, mixed types
• Utility fixtures: temp directories/files, mock Streamlit/pandas objects
• Test data: large datasets for performance testing, parametrized fixtures

Development Workflow

• Commands: Use poetry run pytest to run all tests
• Coverage: Generates HTML reports in htmlcov/, XML reports in coverage.xml
• Markers: Filter tests with -m unit, -m integration, or -m slow

Additional Setup

• Updated .gitignore: Added testing artifacts, Python build files, virtual environments, IDE files
• Validation tests: Created comprehensive validation suite to verify infrastructure works
• Lock file: Generated poetry.lock for reproducible dependency installation

Running Tests

# Install dependencies
poetry install

# Run all tests
poetry run pytest

# Run with coverage (default)
poetry run pytest tests/

# Run only unit tests
poetry run pytest -m unit

# Run integration tests  
poetry run pytest -m integration

# Run without slow tests
poetry run pytest -m "not slow"

# Generate coverage report
poetry run pytest --cov-report=html

Coverage Reports

The setup generates coverage reports in multiple formats:

• Terminal: Shows missing lines during test runs
• HTML: Detailed report in htmlcov/index.html
• XML: Machine-readable report in coverage.xml

Validation

All tests in the validation suite pass, confirming:

• ✅ pytest configuration and test discovery
• ✅ Custom fixtures and markers
• ✅ Coverage reporting setup
• ✅ Mock objects and utilities
• ✅ Temporary file/directory handling
• ✅ Import and dependency resolution

Next Steps

The testing infrastructure is now ready for developers to:

1. Write unit tests in tests/unit/ for individual functions
2. Write integration tests in tests/integration/ for end-to-end workflows
3. Use the provided fixtures for consistent test data
4. Maintain the 80% coverage threshold as new code is added

Files Added/Modified

• pyproject.toml - Poetry configuration and pytest settings
• tests/conftest.py - Comprehensive fixture collection
• tests/test_setup_validation.py - Infrastructure validation tests
• tests/__init__.py, tests/unit/__init__.py, tests/integration/__init__.py - Package structure
• .gitignore - Updated with testing and Python artifacts
• poetry.lock - Dependency lock file