Testing & chaos

Eval scenarios

runEval runs an array of scenarios sequentially. Each scenario creates a fresh GhostEnv from config, runs run(env), then optional assert(env).

import { runEval, defineScenario, github } from "stubfetch";

const report = await runEval([
  defineScenario({
    name: "lists issues",
    config: { providers: [github({ issues: [{ repo: "a/b", title: "t" }] })] },
    run: async (env) => {
      await env.fetch("https://api.github.com/repos/a/b/issues");
    },
    assert: (env) => {
      if (!env.wasCalled("github", { method: "GET" })) throw new Error("expected GET");
    },
  }),
]);

console.log(report.passRate, report.results);

Failures capture error strings per scenario; passRate is ok / count.

Chaos

new GhostEnv({
  seed: 99,
  chaos: {
    minLatencyMs: 50, // await before handler runs
    failureRate: 0.1, // 10% throws before provider
  },
  providers: [/* … */],
});

• failureRate uses the seeded RNG; 0 disables simulated failures (falsy check).
• Failures throw stubfetch chaos: simulated failure (after optional latency).

Recording exports

• exportRecordingJSON — pretty JSON for fixtures or LLM context.
• exportRecordingMarkdown — human-readable sections per call.
• exportHAR — HAR-like JSON (includes extension fields for provider id).

Use these after fetch calls with env.calls().