jest-mock 29.7.0: replaceProperty

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-mock.replaceProperty in pkg:npm/jest-mock@29.7.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/jest-mock@29.7.0
Demonstrate these symbols/APIs:
  - jest-mock.replaceProperty

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-mock-replace-property",
  "version": "1.0.0",
  "private": true,
  "description": "Clean-room verification of jest-mock.replaceProperty",
  "main": "src/index.js",
  "dependencies": {
    "jest-mock": "29.7.0"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify jest-mock.replaceProperty in pkg:npm/jest-mock@29.7.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/jest-mock@29.7.0"
  ],
  "symbols": [
    "jest-mock.replaceProperty"
  ]
}

const { replaceProperty, ModuleMocker } = require('jest-mock');

/**
 * Replace a property on an object with a temporary value.
 * @param {object} object - The target object.
 * @param {string|symbol} propertyKey - The property to replace.
 * @param {*} value - The temporary value.
 * @returns {object} Handle with replaceValue and restore methods.
 */
function replaceObjectProperty(object, propertyKey, value) {
  return replaceProperty(object, propertyKey, value);
}

module.exports = {
  replaceProperty,
  replaceObjectProperty,
  ModuleMocker
};

import assert from 'node:assert';
import { createRequire } from 'node:module';

const require = createRequire(import.meta.url);
const { replaceProperty, replaceObjectProperty, ModuleMocker } = require('../src/index.js');

// 1. replaceProperty replaces the target object property with a temporary value
const target1 = { status: 'initial', count: 1 };
const handle1 = replaceObjectProperty(target1, 'status', 'mocked');
assert.strictEqual(typeof handle1.replaceValue, 'function', 'handle must have replaceValue function');
assert.strictEqual(typeof handle1.restore, 'function', 'handle must have restore function');
assert.strictEqual(target1.status, 'mocked', 'target property should be replaced with new value');
assert.strictEqual(target1.count, 1, 'unmodified properties should remain intact');

// 2. replaceValue updates the temporary replacement value on the target property
handle1.replaceValue('updated_mock');
assert.strictEqual(target1.status, 'updated_mock', 'replaceValue should update the property value');

// 3. restore resets the target property back to its original value
handle1.restore();
assert.strictEqual(target1.status, 'initial', 'restore should reset the property back to original value');

// 4. replaceProperty throws an error when attempting to replace a non-existent property on the target object
const target2 = { existingProp: 'yes' };
assert.throws(
  () => {
    replaceProperty(target2, 'nonExistentProp', 'val');
  },
  {
    name: 'Error',
    message: 'Property `nonExistentProp` does not exist in the provided object'
  },
  'Should throw error when property does not exist on target'
);

// 5. replaceProperty throws an error when called on a primitive value instead of an object
assert.throws(
  () => {
    replaceProperty(null, 'anyProp', 'val');
  },
  {
    name: 'Error',
    message: 'Cannot use replaceProperty on a primitive value; null given'
  },
  'Should throw Error when target is primitive null'
);

assert.throws(
  () => {
    replaceProperty(123, 'anyProp', 'val');
  },
  {
    name: 'Error',
    message: 'Cannot use replaceProperty on a primitive value; number given'
  },
  'Should throw Error when target is primitive number'
);

// 6. replaceProperty throws an error when attempting to replace a function property recommending spyOn instead
const targetFunc = { myMethod: () => 'hello' };
assert.throws(
  () => {
    replaceProperty(targetFunc, 'myMethod', 'val');
  },
  {
    name: 'Error',
    message: "Cannot replace the `myMethod` property because it is a function. Use `jest.spyOn(object, 'myMethod')` instead."
  },
  'Should throw error when target property is a function'
);

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