# CI test runner
URL: /docs/playground/ci-test-runner

Run a suite in a disposable sandbox, watch it fail, apply a fix, watch it pass — then turn the output into a structured report.



A CI job is just a sandbox that clones a repo, runs the tests, and reports back. This workflow
does the smallest honest version of that: a three-assertion suite against an implementation with
a planted bug, a fix applied mid-run, and the raw `node --test` output parsed into the
pass/fail summary a real job would post to a PR.

<WorkflowRunner workflow="ci-test-runner" />

## What just happened [#what-just-happened]

* The project (`package.json`, `sum.js`, `sum.test.js`) was written into `/proj` with
  `sb.writeFile`. `sum.js` subtracts instead of adds.
* `sb.exec("node --test")` ran the suite. Its stdout was streamed live and also captured so the
  step could parse `# pass` / `# fail` counts out of it.
* The fix from the editor overwrote `sum.js` — same `writeFile` call, no new sandbox.
* The suite ran again, green this time, and the final step emitted a JSON report comparing
  before and after.

Everything ran in one container. A real runner would fork per shard — that's the
[Parallel Test Shards](/docs/cookbooks/parallel-test-shards) cookbook, and the
[fork workflow](/docs/playground/fork-a-sandbox) here.