stryker

The stryker command for the System F Software mutation engine — output meant to be read by a program.

Every run writes one NDJSON event per line to stdout and exits with a code that says which thing went wrong, so CI steps and coding agents can act on a run without scraping a progress bar.

Getting started

npm install --save-dev @systemfsoftware/stryker-js-cli
npx stryker run

With a stryker.config.json:

{
  "testRunner": "command",
  "mutate": ["src/**/*.js"],
  "thresholds": { "high": 100, "low": 80, "break": 0 }
}

Requires Node.js 20 or later.

Usage

$ npx stryker <command> [options]

Mutation testing concepts, the supported mutators, and every run option are the ones stryker-mutator.io documents. stryker --llms prints the whole command surface as one JSON object, walked from the command descriptors rather than hand-maintained.

Machine output

$ stryker run
{"kind":"stream","schemaVersion":"1.0","runId":"06FY3DSBM7TYC2RZQ0F3EGVZ88","mode":"machine","signal":"tty"}
{"kind":"phase","phase":"instrument","elapsedMs":102}
{"kind":"phase","phase":"dry-run","elapsedMs":6658}
{"kind":"plan","total":2}
{"kind":"verdict","schemaVersion":"1.0","score":100,"thresholds":{"high":100,"low":80,"break":0},"counts":{"killed":2,"survived":0,"timeout":0,"noCoverage":0},"reportFile":"reports/mutation/mutation.json"}

| kind | Emitted | Carries | | --------- | ----------------------- | --------------------------------------------- | | stream | First line of every run | runId, mode, signal | | phase | A stage begins | phase, elapsedMs | | plan | Mutants scheduled | total | | tick | Progress heartbeat | elapsedMs, completed, total | | verdict | Run finished | score, thresholds, counts, reportFile | | error | Run failed | the failure and a remediation |

The stream drains before the process exits, including on SIGINT, so the terminal line is never truncated.

Machine mode is automatic when stdout is not a TTY. STRYKER_MODE=machine sets it from the environment, and a non-empty AGENT, CLAUDECODE, or CODEX_SANDBOX selects it even on a TTY. NO_COLOR drops colour from the human path.

Exit codes

The highest pending class wins; a terminating signal outranks all of them.

| Code | Meaning | | --------- | -------------------------------------------- | | 0 | Score cleared the break threshold | | 1 | Verdict failed | | 2 | Config error | | 3 | Runtime error | | 4 | Internal error | | 128 + n | Terminated by signal n — SIGINT is 130 |

Related

The mutation engine is @systemfsoftware/stryker-js-platform-node. This package is the terminal-facing half and reaches it through an injected run-event sink; it ships a command and exposes no importable API.

License

Licensed under Apache 2.0.