expect 29.7.0: custom matchers and asymmetric matching with expect.extend

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: custom matchers and asymmetric matching with expect.extend
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/expect@29.7.0
Demonstrate these symbols/APIs:
  - expect.extend

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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import { expect } from 'expect';

/**
 * Custom matchers for numeric ranges, divisibility, and ISO date strings.
 */
export const customMatchers = {
  toBeWithinRange(received, floor, ceiling) {
    const pass = typeof received === 'number' && received >= floor && received <= ceiling;
    return {
      pass,
      message: () =>
        pass
          ? `expected ${received} not to be within range [${floor}, ${ceiling}]`
          : `expected ${received} to be within range [${floor}, ${ceiling}]`
    };
  },
  toBeDivisibleBy(received, divisor) {
    const pass =
      typeof received === 'number' &&
      typeof divisor === 'number' &&
      divisor !== 0 &&
      received % divisor === 0;
    return {
      pass,
      message: () =>
        pass
          ? `expected ${received} not to be divisible by ${divisor}`
          : `expected ${received} to be divisible by ${divisor}`
    };
  },
  toBeValidIsoDate(received) {
    const isString = typeof received === 'string';
    const parsed = isString ? Date.parse(received) : NaN;
    const pass = !Number.isNaN(parsed) && new Date(parsed).toISOString() === received;
    return {
      pass,
      message: () =>
        pass
          ? `expected ${received} not to be a valid ISO 8601 date string`
          : `expected ${received} to be a valid ISO 8601 date string`
    };
  },
  async toBeResolvedWithStatus(receivedPromise, expectedStatus) {
    const resolved = await receivedPromise;
    const pass = resolved !== null && typeof resolved === 'object' && resolved.status === expectedStatus;
    return {
      pass,
      message: () =>
        pass
          ? `expected promise not to resolve with status ${expectedStatus}`
          : `expected promise to resolve with status ${expectedStatus}, received ${resolved ? resolved.status : resolved}`
    };
  }
};

/**
 * Registers custom matchers into expect using expect.extend.
 * @param {Record<string, Function>} [matchers]
 */
export function registerCustomMatchers(matchers = customMatchers) {
  expect.extend(matchers);
}

/**
 * Validates a structured object with asymmetric matchers.
 * @param {object} payload
 * @returns {boolean}
 */
export function validatePayload(payload) {
  expect(payload).toEqual(
    expect.objectContaining({
      id: expect.any(Number),
      name: expect.any(String),
      tags: expect.arrayContaining(['active']),
      metadata: expect.objectContaining({
        version: expect.stringMatching(/^\d+\.\d+$/)
      })
    })
  );
  return true;
}

export { expect };

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{
  "name": "sample-expect-extend",
  "version": "1.0.0",
  "description": "Clean-room verification sample for expect custom matchers with expect.extend",
  "type": "module",
  "main": "index.mjs",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "expect": "29.7.0"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "custom matchers and asymmetric matching with expect.extend",
  "kind": "HOW",
  "packages": [
    "pkg:npm/expect@29.7.0"
  ],
  "symbols": [
    "expect.extend"
  ]
}

import assert from 'node:assert';
import {
  expect,
  customMatchers,
  registerCustomMatchers,
  validatePayload
} from '../index.mjs';

function testExtendRegistersSyncMatchers() {
  registerCustomMatchers();

  // Passing assertions
  expect(15).toBeWithinRange(10, 20);
  expect(10).toBeWithinRange(10, 20);
  expect(20).toBeWithinRange(10, 20);
  expect(12).toBeDivisibleBy(4);
  expect('2026-08-26T00:00:00.000Z').toBeValidIsoDate();

  // Failing assertions throw with expected message
  assert.throws(
    () => {
      expect(25).toBeWithinRange(10, 20);
    },
    (err) => {
      assert.ok(err.message.includes('expected 25 to be within range [10, 20]'));
      return true;
    }
  );

  assert.throws(
    () => {
      expect(13).toBeDivisibleBy(5);
    },
    (err) => {
      assert.ok(err.message.includes('expected 13 to be divisible by 5'));
      return true;
    }
  );

  assert.throws(
    () => {
      expect('not-a-date').toBeValidIsoDate();
    },
    (err) => {
      assert.ok(err.message.includes('expected not-a-date to be a valid ISO 8601 date string'));
      return true;
    }
  );
}

function testExtendSupportsNotModifier() {
  registerCustomMatchers();

  // Inverted passing assertions
  expect(5).not.toBeWithinRange(10, 20);
  expect(25).not.toBeWithinRange(10, 20);
  expect(13).not.toBeDivisibleBy(5);
  expect('invalid-iso-string').not.toBeValidIsoDate();

  // Inverted failing assertion throws
  assert.throws(
    () => {
      expect(15).not.toBeWithinRange(10, 20);
    },
    (err) => {
      assert.ok(err.message.includes('expected 15 not to be within range [10, 20]'));
      return true;
    }
  );
}

async function testExtendRegistersAsyncMatchers() {
  registerCustomMatchers();

  // Async matcher resolves pass
  await expect(Promise.resolve({ status: 200, body: 'ok' })).toBeResolvedWithStatus(200);

  // Async matcher with .not
  await expect(Promise.resolve({ status: 404, body: 'not found' })).not.toBeResolvedWithStatus(200);

  // Async failure throws with message
  let errorCaught = false;
  try {
    await expect(Promise.resolve({ status: 500 })).toBeResolvedWithStatus(200);
  } catch (err) {
    errorCaught = true;
    assert.ok(err.message.includes('expected promise to resolve with status 200, received 500'));
  }
  assert.strictEqual(errorCaught, true, 'Async matcher failure must throw error');
}

function testAsymmetricMatchers() {
  const payload = {
    id: 101,
    name: 'alpha-service',
    tags: ['active', 'internal'],
    metadata: {
      version: '2.5',
      environment: 'production'
    }
  };

  const validated = validatePayload(payload);
  assert.strictEqual(validated, true);

  expect(payload).toEqual(
    expect.objectContaining({
      id: expect.any(Number),
      name: expect.stringContaining('alpha'),
      tags: expect.arrayContaining(['internal'])
    })
  );

  expect('sample-identifier-99').toEqual(expect.stringMatching(/^sample-[a-z]+-\d+$/));
  expect(true).toEqual(expect.anything());

  // Inverted asymmetric matchers
  expect('unrelated-value').toEqual(expect.not.stringContaining('alpha'));
  expect(['a', 'b']).toEqual(expect.not.arrayContaining(['z']));
}

function testAddEqualityTesters() {
  class CustomId {
    constructor(val) {
      this.val = val;
    }
  }

  function customIdTester(a, b) {
    if (a instanceof CustomId && b instanceof CustomId) {
      return a.val === b.val;
    }
    return undefined;
  }

  expect.addEqualityTesters([customIdTester]);

  const id1 = new CustomId('item-42');
  const id2 = new CustomId('item-42');
  const id3 = new CustomId('item-99');

  expect({ id: id1 }).toEqual({ id: id2 });
  assert.throws(() => {
    expect({ id: id1 }).toEqual({ id: id3 });
  });
}

function testStateManagementAndAssertions() {
  const initialState = expect.getState();
  assert.ok(typeof initialState === 'object');

  expect.setState({ customTestTag: 'unit-contract-test' });
  const updatedState = expect.getState();
  assert.strictEqual(updatedState.customTestTag, 'unit-contract-test');

  expect.hasAssertions();
  expect.assertions(1);
  expect(42).toBe(42);
}

async function testResolvesAndRejectsModifiers() {
  await expect(Promise.resolve('expected-result')).resolves.toBe('expected-result');
  await expect(Promise.reject(new Error('operational error'))).rejects.toThrow('operational error');
}

async function runAll() {
  testExtendRegistersSyncMatchers();
  testExtendSupportsNotModifier();
  await testExtendRegistersAsyncMatchers();
  testAsymmetricMatchers();
  testAddEqualityTesters();
  testStateManagementAndAssertions();
  await testResolvesAndRejectsModifiers();

  console.log('Contract tests passed successfully.');
}

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