@vitest/expect 2.1.9: getObjectSubset

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.getObjectSubset 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.getObjectSubset

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 { getObjectSubset } from '@vitest/expect';

/**
 * Extracts a subset of an object matching the shape and keys of a specified subset,
 * counting any omitted properties that were stripped from the source object.
 *
 * @param {unknown} object - Source object or value to extract from.
 * @param {unknown} subset - Target structure specifying which keys to include.
 * @param {Array<Function>} [customTesters=[]] - Optional equality tester functions.
 * @returns {{ subset: unknown, stripped: number }} Result object containing the filtered subset and the count of stripped properties.
 */
export function extractObjectSubset(object, subset, customTesters = []) {
  return getObjectSubset(object, subset, customTesters);
}

export { getObjectSubset };

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{
  "name": "sample-vitest-expect-getobjectsubset",
  "version": "1.0.0",
  "description": "Clean-room verification sample for getObjectSubset in @vitest/expect",
  "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.getObjectSubset in pkg:npm/%40vitest/expect@2.1.9",
  "kind": "HOW",
  "packages": [
    "pkg:npm/%40vitest/expect@2.1.9"
  ],
  "symbols": [
    "@vitest/expect.getObjectSubset"
  ]
}

import assert from 'node:assert/strict';
import { getObjectSubset, extractObjectSubset } from '../index.mjs';

async function runContract() {
  // 1. assert getObjectSubset returns matching subset with zero stripped count when object structurally satisfies subset
  {
    const actual = { a: 1, b: 2, c: 3 };
    const expected = { a: 1 };
    const res = extractObjectSubset(actual, expected, []);
    assert.deepStrictEqual(res, { subset: { a: 1 }, stripped: 0 });

    const identicalActual = { x: 'test', y: true };
    const identicalExpected = { x: 'test', y: true };
    const identicalRes = getObjectSubset(identicalActual, identicalExpected, []);
    assert.deepStrictEqual(identicalRes, { subset: { x: 'test', y: true }, stripped: 0 });
  }

  // 2. assert getObjectSubset filters matching keys and counts stripped properties on mismatched objects
  {
    const actual = { a: 1, b: 2, c: 3 };
    const expected = { a: 99 };
    const res = getObjectSubset(actual, expected, []);
    assert.deepStrictEqual(res, { subset: { a: 1 }, stripped: 2 });
  }

  // 3. assert getObjectSubset recursively trims nested objects and tallies stripped nested properties
  {
    const actual = {
      nested: { x: 10, y: 20, z: 30 },
      topLevelExtra: 'drop-me'
    };
    const expected = {
      nested: { x: 99 }
    };
    const res = getObjectSubset(actual, expected, []);
    assert.deepStrictEqual(res, {
      subset: { nested: { x: 10 } },
      stripped: 3
    });
  }

  // 4. assert getObjectSubset handles arrays of equal length and returns original array on length mismatch
  {
    const actualArray = [{ id: 1, secret: 'hidden' }, { id: 2, secret: 'hidden' }];
    const expectedArray = [{ id: 99 }, { id: 88 }];
    const resArray = getObjectSubset(actualArray, expectedArray, []);
    assert.deepStrictEqual(resArray, {
      subset: [{ id: 1 }, { id: 2 }],
      stripped: 2
    });

    const lengthMismatchActual = [1, 2, 3];
    const lengthMismatchExpected = [1, 2];
    const resMismatch = getObjectSubset(lengthMismatchActual, lengthMismatchExpected, []);
    assert.deepStrictEqual(resMismatch, {
      subset: [1, 2, 3],
      stripped: 0
    });
  }

  // 5. assert getObjectSubset preserves special object types like Date and returns primitive values unchanged
  {
    const testDate = new Date('2026-01-01T00:00:00.000Z');
    const resDate = getObjectSubset(testDate, new Date('2026-01-02T00:00:00.000Z'), []);
    assert.strictEqual(resDate.subset, testDate);
    assert.strictEqual(resDate.stripped, 0);

    const resNumber = getObjectSubset(42, 42, []);
    assert.deepStrictEqual(resNumber, { subset: 42, stripped: 0 });

    const resString = getObjectSubset('hello', 'world', []);
    assert.deepStrictEqual(resString, { subset: 'hello', stripped: 0 });
  }

  // 6. assert getObjectSubset preserves object constructor and supports enumerable Symbol property keys
  {
    class ConfigModel {
      constructor(host, port) {
        this.host = host;
        this.port = port;
      }
    }
    const config = new ConfigModel('localhost', 8080);
    const resConstructor = getObjectSubset(config, { host: 'remotehost' }, []);
    assert.strictEqual(resConstructor.subset.constructor, ConfigModel);
    assert.strictEqual(resConstructor.subset.host, 'localhost');
    assert.strictEqual(resConstructor.stripped, 1);

    const symKey = Symbol('symProp');
    const objWithSym = { name: 'target', [symKey]: 'symVal', extra: 100 };
    const resSym = getObjectSubset(objWithSym, { name: 'diff', [symKey]: 'expectedSym' }, []);
    assert.strictEqual(resSym.subset[symKey], 'symVal');
    assert.strictEqual(resSym.subset.name, 'target');
    assert.strictEqual(resSym.stripped, 1);
  }

  // 7. assert getObjectSubset handles circular references safely without infinite recursion
  {
    const cyclicActual = { id: 1, extra: 'remove' };
    cyclicActual.self = cyclicActual;

    const cyclicExpected = { id: 99, self: null };
    cyclicExpected.self = cyclicExpected;

    const res = getObjectSubset(cyclicActual, cyclicExpected, []);
    assert.strictEqual(res.subset.id, 1);
    assert.strictEqual(res.subset.self, res.subset);
    assert.strictEqual(res.stripped, 1);
  }

  // 8. assert getObjectSubset accepts custom equality testers to evaluate property equivalence
  {
    const caseInsensitiveTester = (a, b) =>
      typeof a === 'string' && typeof b === 'string' ? a.toLowerCase() === b.toLowerCase() : undefined;

    const actual = { role: 'ADMIN', extra: true };
    const expected = { role: 'admin' };
    const res = getObjectSubset(actual, expected, [caseInsensitiveTester]);
    assert.deepStrictEqual(res, { subset: { role: 'admin' }, stripped: 0 });
  }

  // 9. assert getObjectSubset throws TypeError when customTesters is not iterable
  {
    assert.throws(
      () => getObjectSubset({ a: 1 }, { a: 1 }),
      (err) => err instanceof TypeError && /not iterable/.test(err.message)
    );
  }

  console.log('All @vitest/expect.getObjectSubset contract assertions passed successfully.');
}

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