pytest runs in CI on every push and pull request

[HughRunyan]

Output

SWEET_python's tests/ directory gets run by CI. It has held 8 test files and no
workflow that runs them; .github/workflows/ contained only jira_ticket.yml.

As a SWEET_python contributor, I want the test suite to run on every push
and pull request so that a model change that breaks an existing test is caught
here, in the repo that owns the code — and so that tests of this package's
internals can live here at all.

Why now

Because nothing gated them, model unit tests have been getting written in
WasteMAP's backend/tests/fast/ instead — the only repo of the pair with test CI.
That forces WasteMAP's suite to import private SWEET_python helpers, e.g.
SWEET_python.advanced_dst_city._prevent_food_waste, which Copilot flagged on
RMI/WasteMAP#772. With a test workflow here, those tests have somewhere better to
go.

I checked the existing tests before adding the gate

They are all fine. 133 tests, all passing on Python 3.12 against the pinned
lockfile — nothing stale, nothing disabled, nothing excluded:

File	Tests
test_dst_allocation.py	58	pass
test_mcf.py	22	pass
test_flare_slip_and_capture_bounds.py	19	pass
test_mass_checker_integration.py	18	pass
test_food_waste_prevention.py	8	pass
test_model_v2_oxidation_emission_year.py	3	pass
test_sdst_v1_5_preimplement_composition.py	3	pass
test_model_v2_years.py	2	pass

None of them needs a database, network access or an environment variable. I
verified that rather than assuming it: with socket.connect, connect_ex,
getaddrinfo and create_connection all replaced by a raising stub, the full
suite still passes in 2.7s. Grepping the suite agrees — the only pytest.mark
usage anywhere in tests/ is parametrize, and there is no skipif, no
os.environ, and no DB driver import.

So the fast/integration split this workflow sets up has nothing in its integration
half yet. That is the honest state of the repo, not a shortcut.

What the workflow does

pytest -m "not integration" on Python 3.12, on push and pull_request.
Roughly 50s end to end, of which the tests are 4s.

• Python 3.12 matches WasteMAP's CI and deploy images, which is where this
  package actually executes. (The code needs 3.10+ for PEP 604 annotations, so
  3.12 is a match to reality, not a floor this workflow invents.)
• Installs the pinned requirements.txt, which is what that lockfile says it
  exists for. It then installs the package itself with --no-deps -e ., so
  import SWEET_python resolves to the checkout and setup.py's packaging gets
  exercised on the way.
• libpq-dev is installed because psycopg2 (not psycopg2-binary)
  publishes no manylinux wheel — pip builds it from source and needs pg_config.
  Confirmed necessary: the CI log shows Building wheel for psycopg2 taking ~6s.
• pytest is bounded, not pinned (>=8,<10): minor and patch releases are
  welcome, a major one should not break CI on a day nobody touched the model.
• pytest.ini registers the integration marker and sets testpaths = tests
  (so dst_allocation_prototype.py, the ~400k-case fuzz harness at the repo root,
  is never collected) and --strict-markers, so a mistyped
  @pytest.mark.integraton is a collection error instead of a test that silently
  keeps running in the fast job. All three behaviours are verified with a
  throwaway probe test.
• Action versions are the current majors (checkout@v7, setup-python@v7);
  v4/v5 target Node 20 and produce a deprecation annotation. Dependabot already
  covers github-actions here, so they will stay current.

This complements WasteMAP's CI, it does not replace it

WasteMAP's tests.yml installs a SWEET_python branch with the same name as
the WasteMAP branch under test, so a model change here and its WasteMAP consumer
are already exercised as a pair over there. What that pairing never did is run
this repo's own tests. That is the gap, and it is why the trigger is
[push, pull_request] rather than PR-only: a SWEET_python branch is routinely
pushed to pair with a same-named WasteMAP branch before either has a PR, and those
pushes should be gated too. The cost is that a branch with an open PR in this repo
runs twice for the same commit — cheap for a 4-second suite, and easy to trim to
push: branches: [main] if the second check is unwelcome.

Deliberately not here

• No changelog entry. changelog/ tracks model and methodology change — every
  existing entry is model behaviour, flagged for output effects. A test runner
  changes no output and tells a WasteMAP or Climate TRACE consumer nothing. Happy
  to add a line if you read the convention more broadly.
• No integration job. There are no integration tests to put in it; a job that
  collects nothing exits 5. The marker is live the moment one is written, and the
  first one should get its own job rather than a database bolted onto this one.
• No Python matrix. 3.12 is what ships. A matrix is cheap to add later if this
  package ever needs to support a range.

Follow-up (not in this PR)

The five _prevent_food_waste unit tests in WasteMAP's
backend/tests/fast/test_advanced_dst_city_food_prevention.py are now movable
here, which would let that private import be dropped. The reasoning for keeping it
for now is recorded in a comment above the import (WasteMAP commit 621f11f6);
that comment should be revisited once this merges.

Acceptance criteria

• A GitHub Actions workflow runs pytest on push and pull_request.
• It runs on Python 3.12.
• Every existing test is accounted for: 133 pass, none disabled, none skipped.
• Tests needing a database or network are excluded from the fast job by a
  registered integration marker; the exclusion, the opt-in and the
  strict-marker error are all verified.
• The workflow is green on this branch.
• Contributor docs say how to run the suite and where an integration test goes.

Definition of Done

• Acceptance criteria met
• Tests and checks pass (Tests / Fast tests green on this branch)
• Docs updated (README gains a # Tests section)
• Reviewed and merged

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🤖 Generated with Claude Code

[Copilot]

🟢 Approval recommended

The workflow/config additions satisfy the stated CI goal, with only a minor documentation tweak suggested for reproducible local installs.

Pull request overview

This PR adds first-class CI coverage for SWEET_python’s existing pytest suite by introducing a GitHub Actions workflow that runs on every push and pull request, along with the minimal pytest configuration and contributor documentation needed to support it.

Changes:

• Add a GitHub Actions workflow to run pytest -m "not integration" on Python 3.12 for push and pull_request.
• Add pytest.ini to scope test collection to tests/ and register the integration marker with strict marker checking.
• Document how to run tests locally and how to mark future integration tests in the README.

File summaries

File	Description
README.md	Adds a “Tests” section describing local test execution and the fast/integration marker split.
pytest.ini	Configures pytest collection (testpaths) and enables --strict-markers with an integration marker registration.
.github/workflows/tests.yml	Introduces CI to install deps and run fast pytest on pushes and PRs using Python 3.12.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Lite

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