ci-demo-python

A tiny, dependency-free stock portfolio domain model in Python, used as a live example in a Continuous Integration training session. No web framework, no database, no external services — just business rules and the tests that pin them down, wired to a GitHub Actions pipeline that blocks merging into main when a test fails.

What's here

portfolio_domain/
  money.py       Money value object (immutable, rounds to 2 decimals)
  portfolio.py   Portfolio aggregate: deposit / buy / sell shares, FIFO lots
  exceptions.py  Domain errors (insufficient funds / insufficient shares)
tests/
  test_money.py
  test_portfolio.py
.github/workflows/ci.yml   Runs the full test suite on every push and PR

Running it locally

python3 -m venv .venv
source .venv/bin/activate        # Windows: .venv\Scripts\activate
pip install -r requirements.txt
pytest -v

All 15 tests run in well under a second — no Docker, no network, no database.

The point of this repo

main is protected: a pull request cannot be merged while the Run domain tests check is failing. Try it yourself:

1. Create a branch.
2. Break something in portfolio_domain/portfolio.py (or "fix" a test to expect the wrong thing).
3. Push the branch and open a pull request against main.
4. Watch the check turn red — the Merge button is disabled.
5. Fix the code, push again — the check turns green and the PR becomes mergeable.

• DEMO_SCRIPT.md — condensed, copy-paste-ready run sheet for the live walkthrough above.
• docs/WALKTHROUGH.md — the same walkthrough fully explained, with diagrams, plus a follow-up exercise to repeat the whole thing on your own fork afterwards.

License

MIT — see LICENSE.