@vitest/expect 2.1.9: JestChaiExpect

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 @vitest/expect.JestChaiExpect in pkg:npm/%40vitest/expect@2.1.9
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/%40vitest/expect@2.1.9
Demonstrate these symbols/APIs:
  - @vitest/expect.JestChaiExpect

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 * as chai from 'chai';
import {
  JestChaiExpect,
} from '@vitest/expect';

// Register the JestChaiExpect plugin on chai
chai.use(JestChaiExpect);

export const expect = chai.expect;

/**
 * Registers the JestChaiExpect plugin on a given Chai instance.
 *
 * @param {object} chaiInstance - The Chai instance to register the plugin with.
 * @returns {object} The Chai instance with Jest matchers attached.
 */
export function registerJestChaiExpect(chaiInstance) {
  chaiInstance.use(JestChaiExpect);
  return chaiInstance;
}

export {
  JestChaiExpect,
};

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{
  "name": "sample-vitest-expect-jest-chai-expect",
  "version": "1.0.0",
  "description": "Clean-room verification sample for @vitest/expect JestChaiExpect",
  "type": "module",
  "main": "index.mjs",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "license": "MIT-0",
  "dependencies": {
    "@vitest/expect": "2.1.9"
  }
}

{
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  "goal": "verify @vitest/expect.JestChaiExpect in pkg:npm/%40vitest/expect@2.1.9",
  "kind": "HOW",
  "packages": [
    "pkg:npm/%40vitest/expect@2.1.9"
  ],
  "symbols": [
    "@vitest/expect.JestChaiExpect"
  ]
}

import assert from 'node:assert/strict';
import * as chai from 'chai';
import {
  expect,
  JestChaiExpect,
  registerJestChaiExpect,
} from '../index.mjs';

async function runContract() {
  // 1. assert JestChaiExpect is a function Chai plugin that registers Jest matchers onto chai.Assertion.prototype and chai.expect
  assert.strictEqual(typeof JestChaiExpect, 'function');
  assert.strictEqual(typeof expect, 'function');

  // Verify Chai registration helper
  const registered = registerJestChaiExpect(chai);
  assert.strictEqual(registered, chai);
  assert.strictEqual(typeof chai.Assertion.prototype.toBe, 'function');
  assert.strictEqual(typeof chai.Assertion.prototype.toEqual, 'function');
  assert.strictEqual(typeof chai.Assertion.prototype.toStrictEqual, 'function');
  assert.strictEqual(typeof chai.Assertion.prototype.toBeTruthy, 'function');
  assert.strictEqual(typeof chai.Assertion.prototype.toBeFalsy, 'function');
  assert.strictEqual(typeof chai.Assertion.prototype.toMatchObject, 'function');

  // 2. assert toBe validates primitive and referential equality using Object.is and rejects mismatched values
  expect(42).toBe(42);
  expect('alpha').toBe('alpha');
  expect(true).toBe(true);
  const objRef = { id: 1 };
  expect(objRef).toBe(objRef);
  assert.throws(() => expect(42).toBe(43), /AssertionError/);
  assert.throws(() => expect({ id: 1 }).toBe({ id: 1 }), /AssertionError/);

  // 3. assert toEqual performs deep equality comparison across objects arrays and nested structures
  expect({ x: 1, y: [10, 20] }).toEqual({ x: 1, y: [10, 20] });
  expect(['a', 'b', { c: 3 }]).toEqual(['a', 'b', { c: 3 }]);
  assert.throws(() => expect({ x: 1 }).toEqual({ x: 2 }), /AssertionError/);

  // 4. assert toStrictEqual performs strict equality checking types prototype and undefined properties
  class ModelA {
    constructor(val) {
      this.val = val;
    }
  }
  class ModelB {
    constructor(val) {
      this.val = val;
    }
  }
  expect(new ModelA('test')).toStrictEqual(new ModelA('test'));
  assert.throws(() => expect(new ModelA('test')).toStrictEqual(new ModelB('test')), /AssertionError/);
  assert.throws(() => expect({ a: undefined, b: 1 }).toStrictEqual({ b: 1 }), /AssertionError/);

  // 5. assert toBeTruthy and toBeFalsy evaluate boolean truthiness of values
  expect('truthy string').toBeTruthy();
  expect(100).toBeTruthy();
  expect({}).toBeTruthy();
  expect(0).toBeFalsy();
  expect('').toBeFalsy();
  expect(null).toBeFalsy();
  expect(undefined).toBeFalsy();
  assert.throws(() => expect(false).toBeTruthy(), /AssertionError/);
  assert.throws(() => expect(true).toBeFalsy(), /AssertionError/);

  // 6. assert toBeNull toBeUndefined toBeDefined and toBeNaN evaluate precise primitive states
  expect(null).toBeNull();
  expect(undefined).toBeUndefined();
  expect('defined value').toBeDefined();
  expect(Number.NaN).toBeNaN();
  assert.throws(() => expect(undefined).toBeNull(), /AssertionError/);
  assert.throws(() => expect(null).toBeUndefined(), /AssertionError/);
  assert.throws(() => expect(undefined).toBeDefined(), /AssertionError/);
  assert.throws(() => expect(123).toBeNaN(), /AssertionError/);

  // 7. assert toBeGreaterThan toBeGreaterThanOrEqual toBeLessThan and toBeLessThanOrEqual compare numeric values
  expect(20).toBeGreaterThan(10);
  expect(20).toBeGreaterThanOrEqual(20);
  expect(10).toBeLessThan(20);
  expect(10).toBeLessThanOrEqual(10);
  assert.throws(() => expect(5).toBeGreaterThan(10), /AssertionError/);
  assert.throws(() => expect(15).toBeLessThan(10), /AssertionError/);

  // 8. assert toMatch validates string substrings and regular expressions
  expect('code-sample-x').toMatch('sample');
  expect('sample-12345').toMatch(/^sample-\d{5}$/);
  assert.throws(() => expect('sample-abc').toMatch(/\d+/), /AssertionError/);

  // 9. assert toMatchObject validates partial object properties against target objects
  const payload = {
    id: 'req_123',
    status: 'active',
    metadata: { env: 'production', region: 'us-west' },
  };
  expect(payload).toMatchObject({
    status: 'active',
    metadata: { env: 'production' },
  });
  assert.throws(() => expect(payload).toMatchObject({ status: 'pending' }), /AssertionError/);

  // 10. assert toContain validates element inclusion in arrays and substring inclusion in strings
  expect([1, 2, 3, 4]).toContain(3);
  expect('vitest testing framework').toContain('testing');
  assert.throws(() => expect([1, 2]).toContain(5), /AssertionError/);
  assert.throws(() => expect('vitest').toContain('jest'), /AssertionError/);

  // 11. assert toContainEqual validates element presence in arrays using deep equality
  const itemList = [{ id: 1, name: 'first' }, { id: 2, name: 'second' }];
  expect(itemList).toContainEqual({ id: 1, name: 'first' });
  assert.throws(() => expect(itemList).toContainEqual({ id: 3, name: 'third' }), /AssertionError/);

  // 12. assert toHaveLength validates the length property of collections and strings
  expect(['a', 'b', 'c']).toHaveLength(3);
  expect('length-check').toHaveLength(12);
  assert.throws(() => expect([1, 2]).toHaveLength(5), /AssertionError/);

  // 13. assert toHaveProperty validates property existence and value at specified object key paths
  const config = {
    server: {
      host: 'localhost',
      port: 8080,
    },
  };
  expect(config).toHaveProperty('server.host', 'localhost');
  expect(config).toHaveProperty('server.port');
  assert.throws(() => expect(config).toHaveProperty('server.ssl'), /AssertionError/);

  // 14. assert toThrow validates function error throwing with message patterns and error constructors
  const throwError = () => {
    throw new RangeError('Index out of range');
  };
  expect(throwError).toThrow('out of range');
  expect(throwError).toThrow(RangeError);
  expect(throwError).toThrow(/Index/);
  assert.throws(() => expect(() => {}).toThrow(), /AssertionError/);

  // 15. assert negation modifier not inverts matchers correctly across assertions
  expect(10).not.toBe(20);
  expect({ a: 1 }).not.toEqual({ a: 2 });
  expect('hello').not.toContain('world');
  expect(() => {}).not.toThrow();
  assert.throws(() => expect(10).not.toBe(10), /AssertionError/);

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

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