CI & modes

How the mode is chosen

The first match wins:

1. mode= argument, or beacon.snapshots.configure(mode=...)
2. pytest --beacon-snapshot=new|check|update
3. BEACON_SNAPSHOT_MODE environment variable
4. check if CI is set (to anything but 0/false/no), otherwise new

So on GitHub Actions, GitLab CI and most other providers (which set CI=true), a missing snapshot fails the build. You can’t forget to commit one.

Note

These settings only change what the test harness does with files. Block output never depends on them.

Line endings

Snapshots are compared byte for byte, so stop git from rewriting them on Windows checkouts:

.gitattributes

snapshots/** text eol=lf

beacon tolerates CRLF when reading, but always writes LF.

GitHub Actions

.github/workflows/test.yml

name: tests
on: [push, pull_request]
jobs:
  test:
    strategy:
      matrix:
        os: [ubuntu-latest, macos-latest, windows-latest]
    runs-on: ${{ matrix.os }}
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python@v5
        with:
          python-version: "3.12"
      - run: pip install -e . llm-beacon pytest
      - run: pytest        # CI=true → snapshot mode "check"

Running the same snapshots on all three operating systems is the strongest determinism test you can have. beacon’s own CI does exactly this for its 111 golden files.

Reviewing changes

When a snapshot changes intentionally:

python -m beacon.snapshots update
git diff snapshots/

Read the diff before committing. It’s a precise record of how your app’s behaviour changed.