feat: Add comprehensive Python testing infrastructure with Poetry

[llbbl]

Add Python Testing Infrastructure

Summary

This PR sets up a comprehensive testing infrastructure for the Udemy Downloader CLI project using Poetry as the package manager and pytest as the testing framework.

Changes Made

Package Management

• Migrated to Poetry: Created pyproject.toml with Poetry configuration
• Migrated dependencies: All dependencies from requirements.txt are now managed by Poetry
• Lock file support: Poetry will generate poetry.lock for reproducible builds

Testing Framework

• pytest: Main testing framework with extensive configuration
• pytest-cov: Coverage reporting with 80% threshold requirement
• pytest-mock: Mocking utilities for unit tests

Configuration

Added comprehensive pytest configuration in pyproject.toml:

• Test discovery patterns for test_*.py and *_test.py files
• Coverage settings with HTML and XML report generation
• Custom test markers: @pytest.mark.unit, @pytest.mark.integration, @pytest.mark.slow
• Strict mode enabled for better test quality

Test Structure

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

Test Fixtures

Created comprehensive fixtures in conftest.py:

• temp_dir: Temporary directory management
• mock_settings: Mock configuration data
• mock_course_data / mock_lecture_data: Mock Udemy data
• mock_response / mock_failed_response: HTTP response mocking
• mock_cloudscraper: CloudScraper session mocking
• mock_browser_cookies: Browser cookie mocking
• capture_logs: Log output capture
• mock_gui_window: FreeSimpleGUI window mocking
• And more...

Updated .gitignore

Added entries for:

• Testing artifacts (.pytest_cache/, coverage.xml, htmlcov/)
• Poetry artifacts (keeping poetry.lock tracked)
• Claude settings (.claude/*)
• Virtual environments and Python artifacts

Running Tests

Install dependencies:

poetry install

Run tests:

# Using Poetry scripts (both commands work)
poetry run test
poetry run tests

# Or directly with pytest
poetry run pytest

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

# Run with coverage report
poetry run pytest --cov

View coverage report:

# HTML report will be in htmlcov/index.html
open htmlcov/index.html

Notes

• The testing infrastructure is now ready for developers to write unit and integration tests
• Coverage threshold is set to 80% - tests will fail if coverage drops below this
• The validation test (test_validation.py) verifies that all testing components are properly configured
• GUI tests may fail in headless environments due to display requirements
• No actual unit tests for the codebase were written - only infrastructure setup

Next Steps

1. Write unit tests for individual modules (base.py, cli.py, etc.)
2. Write integration tests for end-to-end workflows
3. Set up CI/CD pipeline to run tests automatically
4. Consider adding additional testing tools (e.g., pytest-asyncio for async code, pytest-xdist for parallel execution)