fixes #478

Summary

Adds comprehensive test infrastructure with CI/CD for all Python packages in the Cua project.

Changes included:

Test Infrastructure Setup:

• Added separate tests/ directories for all 7 Python packages (core, agent, computer, computer-server, mcp-server, pylume, som)
• Created 30+ unit tests with full mocking of external dependencies (liteLLM, PostHog, Computer interfaces)
• Added conftest.py fixtures in each package for shared test setup and dependency mocking
• All tests run in <15 seconds with no external API calls or secrets required

CI/CD Integration:

• Added GitHub Actions workflow (.github/workflows/python-tests.yml) to run tests on all PRs and pushes to main
• Implemented matrix strategy to test each package independently in parallel
• Python 3.12 testing with ~2 minute total runtime
• Validates code quality before merging

Documentation:

• Added concise TESTING.md with quick start guide, architecture principles, and troubleshooting tips
• Documents how to run tests locally and add new tests following SOLID principles

Architecture:

• Single Responsibility Principle: Each package tests only its own code, each test file tests one feature
• Vertical Slice Architecture: Tests organized by domain/feature, not by test type
• Testability: All external dependencies mocked for fast, isolated testing

Impact:

• All future PRs will automatically run 30+ unit tests before merging
• Developers can run tests locally in seconds with simple pytest commands
• Test coverage for core functionality without API costs or secrets management
• Foundation for expanding test coverage as new features are added

Test Results:

core package: 20/20 tests passing (100%)
agent package: 10/10 tests passing (100%)
computer: Smoke tests passing
computer-server: Smoke tests passing
mcp-server: Smoke tests passing
pylume: Smoke tests passing

How to Test

Run all tests:

# Set environment variable
$env:CUA_TELEMETRY_DISABLED="1"  # Windows
export CUA_TELEMETRY_DISABLED=1  # Linux/Mac

# Run tests
pytest libs/python/*/tests/ -v

Final thoughts

I was thinking about stuff like: Coverage Metrics to add to workflow for long-term or Pre-commit Hooks for devops stuff but I figured I'd listen to feedback first.

About this contribution

I'm interested in contributing more to Cua and be considered for the Founding Engineer role.
This PR demonstrates:

• Infrastructure thinking (CI/CD pipeline design)
• Python proficiency across multiple packages
• Developer experience focus (fast tests, clear docs)
• Understanding of SOLID principles and testing best practices

Thanks!