reproducing-ci-locally

Reproducing CI Locally

A local check is only useful if it runs the same thing the runner runs. Most "green locally, red in CI" failures are not bugs in the code — they are a difference between two commands: different paths, different test markers, different env, a different linter version, or a different interpreter.

The fix is mechanical: derive the local command from the workflow file, not from the Makefile, not from habit, not from what the last repo used.

Read the workflow before you run anything

The workflow is the contract. The Makefile is a convenience that drifts from it.

# What the gate actually is, in order
sed -n '/jobs:/,$p' .github/workflows/ci.yml

# Every command CI runs, across all workflows
grep -rn "run:" .github/workflows/

Copy out four things, verbatim:

1. The commands and their order.
2. The paths each command is scoped to (ruff check app tests scripts is not ruff check .).
3. Test selection — marker expressions, -k filters, which suites are excluded.
4. The env: block, and the runtime/toolchain versions in setup-* steps.

Each of those four is a distinct way to get a wrong answer locally.

Paths. If CI lints app tests scripts and you run ruff check ., you get findings from directories CI never looks at — a red that isn't a merge blocker and shouldn't be "fixed" in an unrelated PR. Run it the narrow way to reproduce the gate; run it the wide way only when you're deliberately auditing.

Markers. A suite-wide make test that excludes one marker is not the CI gate if CI excludes six. Live-credential integration tests deselected in CI will run locally, hit a fake key, and fail in a way that looks like a regression:

# Wrong: local shorthand — pulls in suites CI never runs
pytest -m "not browser"

# Right: the full expression, copied from the workflow
pytest -m "not browser and not slow and not load and not integration"

Env. Config objects instantiated at import time (a settings singleton at module scope, an engine built when the module loads) make collection fail without the workflow's variables — a wall of "Field required" errors that looks like a broken suite. Mirror the env: block, including the shape of values: if CI passes a Postgres URL and the module builds a pooled engine, a local SQLite URL raises on arguments that dialect rejects before a single test runs.