Run your test suite

Run your application's assertions against selected twins, using the same SDK calls as production. This complete example uses Node's test runner, a local Stripe twin and no real vendor credentials. Use Node 22.6 or newer and npm; installing packages needs registry access.

Save the app and its testCopy Anchor Link

In an empty directory, save package.json:

{
  "name": "signup-tests",
  "private": true,
  "type": "module",
  "scripts": { "test": "node --test --test-reporter=tap signup.test.mjs" },
  "dependencies": { "stripe": "17.7.0" },
  "devDependencies": {
    "@volter/world": "3.0.63",
    "@volter/twin-stripe": "3.0.1"
  }
}

Save .env.example, with an empty value:

STRIPE_SECRET_KEY=

Save signup.test.mjs:

import { test } from 'node:test';
import assert from 'node:assert/strict';
import Stripe from 'stripe';

test('signup stores a retrievable customer', async () => {
  const stripe = new Stripe(process.env.STRIPE_SECRET_KEY);
  const created = await stripe.customers.create({ email: 'ada@example.com', name: 'Ada' });
  const saved = await stripe.customers.retrieve(created.id);
  assert.equal(saved.id, created.id);
  assert.equal(saved.email, 'ada@example.com');
  assert.equal(saved.name, 'Ada');
});

The test checks a stored result through the real SDK; a fabricated success response alone would not pass it. Choose a twin explains selecting an implementation for these calls.

Run the suite inside the WorldCopy Anchor Link

npm install
npx volter world init --name signup-tests
npx volter world up
npx volter world clock set 2026-01-15T12:00:00Z
npx volter world run -- npm test

# pass 1
# fail 0

run supplies fake credentials and routes selected SDK destinations. The World stays up after the command finishes; its state accumulates between commands until you reset it.

Inspect the writesCopy Anchor Link

npx volter world log
npx volter world diff

customer.create
event.record

SDK reads verify records; the log tells you which stored operations the app performed. It is not a line-coverage report or a transcript of every read. Inspect a World adds the dashboard and vendor screens.

Repeat from known dataCopy Anchor Link

Reset before the next suite run and set the same starting clock:

npx volter world reset
npx volter world clock set 2026-01-15T12:00:00Z
npx volter world run -- npm test

# pass 1
# fail 0

Create stored prerequisites through the vendor API in your setup or project-owned seed. Seed and reset makes that starting data repeatable. Use separate World roots for concurrent suites that must not share mutations; do not reset a World another test uses.

For a scripted answer, rate-limit error or retry path, see shape the World for a test. Freeze time before TTL assertions and advance it explicitly. Generative twins check calls and state effects; they do not assess the prose quality of a real model.

Other runners and browser testsCopy Anchor Link

Replace npm test with your own Node runner's command. A Bun test runner needs its injector armed as described in the CLI reference; install the imported kernel package in the app, since a global CLI does not supply app dependencies. Non-Node programs and browser-side vendor requests need their supported routing path; see route a CLI and run a full stack.

Catalog assessment measures its published journeys. Your application suite measures your own requirements; passing either does not prove every vendor operation or state works.

StopCopy Anchor Link

npx volter world down

Stopped signup-tests

Stop application consumers before the World. Ordinary shutdown retains data. Use in CI runs the same commands with cleanup after success or failure.