jest-worker 30.4.1: messageParent

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify jest-worker.messageParent in pkg:npm/jest-worker@30.4.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/jest-worker@30.4.1
Demonstrate these symbols/APIs:
  - jest-worker.messageParent

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

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{
  "name": "sample-jest-worker-messageparent",
  "version": "1.0.0",
  "private": true,
  "description": "verify jest-worker.messageParent in pkg:npm/jest-worker@30.4.1",
  "main": "src/index.js",
  "scripts": {
    "test": "node test/contract.cjs"
  },
  "dependencies": {
    "jest-worker": "30.4.1"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "verify jest-worker.messageParent in pkg:npm/jest-worker@30.4.1",
  "kind": "HOW",
  "packages": [
    "pkg:npm/jest-worker@30.4.1"
  ],
  "symbols": [
    "jest-worker.messageParent"
  ]
}

'use strict';

const path = require('node:path');
const { Worker, messageParent } = require('jest-worker');

/**
 * Sends a message to parent process or throws TypeError if not in worker context.
 * @param {unknown} message
 * @param {NodeJS.Process} [parentProcess]
 */
function sendMessageToParent(message, parentProcess) {
  return messageParent(message, parentProcess);
}

/**
 * Runs a worker task using Worker pool and collects custom messages sent via messageParent.
 * @param {string} taskName
 * @param {number} steps
 * @returns {Promise<{ result: string, customMessages: Array<unknown> }>}
 */
async function runWorkerWithProgress(taskName, steps = 2) {
  const workerPath = path.resolve(__dirname, 'worker.js');
  const worker = new Worker(workerPath, {
    numWorkers: 1,
    enableWorkerThreads: true,
    exposedMethods: ['processTask'],
  });

  const customMessages = [];
  try {
    const taskPromise = worker.processTask(taskName, steps);
    if (typeof taskPromise.UNSTABLE_onCustomMessage === 'function') {
      taskPromise.UNSTABLE_onCustomMessage((msg) => {
        customMessages.push(msg);
      });
    }
    const result = await taskPromise;
    return { result, customMessages };
  } finally {
    await worker.end();
  }
}

module.exports = {
  sendMessageToParent,
  runWorkerWithProgress,
  messageParent,
};

'use strict';

const { messageParent } = require('jest-worker');

/**
 * Worker task function that sends progress updates using messageParent.
 * @param {string} taskName
 * @param {number} steps
 * @returns {Promise<string>}
 */
async function processTask(taskName, steps = 2) {
  for (let step = 1; step <= steps; step++) {
    messageParent({
      taskName,
      step,
      totalSteps: steps,
      status: 'in_progress',
    });
  }

  messageParent({
    taskName,
    step: steps,
    totalSteps: steps,
    status: 'complete',
  });

  return `completed:${taskName}`;
}

module.exports = {
  processTask,
};

'use strict';

const assert = require('node:assert/strict');
const { messageParent } = require('jest-worker');
const {
  sendMessageToParent,
  runWorkerWithProgress,
} = require('../src/index.js');

async function testContract() {
  // 1. jest-worker exports messageParent function
  assert.equal(typeof messageParent, 'function', 'messageParent must be an exported function');
  assert.strictEqual(typeof sendMessageToParent, 'function', 'sendMessageToParent helper must be a function');

  // 2. messageParent throws TypeError when called outside worker thread or process with no parentPort or send method
  let errorThrown = false;
  try {
    messageParent({ type: 'test-event' });
  } catch (err) {
    errorThrown = true;
    assert(err instanceof TypeError, 'Error must be an instance of TypeError');
    assert.strictEqual(
      err.message,
      '"messageParent" can only be used inside a worker',
      'TypeError message must match expected worker context restriction'
    );
  }
  assert.strictEqual(errorThrown, true, 'messageParent must throw when executed outside worker environment');

  // 3. messageParent sends custom message tuple [3, payload] via custom parentProcess send function
  const receivedMessages = [];
  const mockParentProcess = {
    send(payload) {
      receivedMessages.push(payload);
    },
  };
  const testPayload = { event: 'heartbeat', timestamp: 12345 };
  sendMessageToParent(testPayload, mockParentProcess);

  assert.strictEqual(receivedMessages.length, 1, 'Custom parent process should receive exactly one message');
  assert.strictEqual(receivedMessages[0][0], 3, 'First element of tuple must be PARENT_MESSAGE_CUSTOM (3)');
  assert.deepStrictEqual(receivedMessages[0][1], testPayload, 'Second element must be the payload');

  // 4. messageParent dispatches progress messages from a worker task to the parent process via UNSTABLE_onCustomMessage
  const { result, customMessages } = await runWorkerWithProgress('job-alpha', 2);
  assert.strictEqual(result, 'completed:job-alpha', 'Worker should successfully finish the task');
  assert.strictEqual(customMessages.length, 3, 'Should receive 2 in-progress messages and 1 complete message');

  // 5. messageParent delivers multiple sequential messages before task resolution in a Worker pool
  assert.deepStrictEqual(customMessages[0], {
    taskName: 'job-alpha',
    step: 1,
    totalSteps: 2,
    status: 'in_progress',
  });
  assert.deepStrictEqual(customMessages[1], {
    taskName: 'job-alpha',
    step: 2,
    totalSteps: 2,
    status: 'in_progress',
  });
  assert.deepStrictEqual(customMessages[2], {
    taskName: 'job-alpha',
    step: 2,
    totalSteps: 2,
    status: 'complete',
  });

  console.log('Contract assertions verified successfully.');
}

testContract().catch((err) => {
  console.error('Contract test failed:', err);
  process.exit(1);
});