Actor checker API

Install fast-check in the project that runs the checks with bun add -d fast-check, then import from tardie/testing. The runtime package declares fast-check as an optional peer dependency. Full example.

checkActor

const report = await checkActor(actor, {
  inputs,                 // arbitrary of { method, input }
  services: testServices,  // context => Effect Layer
  invariants: rules,
  numRuns: 100,
  maxSteps: 100,
  timeoutMs: 5_000,
  seed: 42,               // optional
})

Each case starts fresh. services supplies fake, real, or mixed dependencies. context.generate(builder, ...args) records choices for shrinking and replay. Keep its call order stable.

DEFAULT_ACTOR_CHECK exports the defaults. The report contains status, seed, numRuns, boundedRuns, and policy. "passed" means rest without a violation; "bounded" means a run reached its step limit. Rest can mean waiting for input. The step bound does not prevent an effect already running.

Rules

import type { Event } from "tardie/core"

type Rule = (context: {
  readonly events: ReadonlyArray<Event>
}) => void | boolean

invariants maps names to synchronous rules. Each receives a copy of [], [e1], [e1, e2], and so on. false or a throw fails; true or void passes.

Failures and replay

ActorCheckError carries counterexample, seed, and numShrinks. Its events end at the first rule violation; example holds the input and generated choices.

const replay = await replayActor(actor, error.counterexample.example, {
  services: testServices,
  invariants: rules,
})

Replay returns status, steps, events, example, and optional failure. Generated choices replay; ordinary service calls run again. Services must be deterministic to reproduce a failure.

The checker covers one invocation; cross-thread delivery and child allocation fail explicitly. Passing provides evidence for sampled executions, without proving every possible execution safe.