jest-matcher-utils 29.7.0: matcherHint, printExpected, printReceived

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.

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Goal: verify pkg:npm/jest-matcher-utils@29.7.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/jest-matcher-utils@29.7.0

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-matcher-utils-verify",
  "version": "1.0.0",
  "private": true,
  "description": "verify pkg:npm/jest-matcher-utils@29.7.0",
  "main": "src/index.js",
  "scripts": {
    "test": "node test/contract.js"
  },
  "dependencies": {
    "jest-matcher-utils": "29.7.0"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:npm/jest-matcher-utils@29.7.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/jest-matcher-utils@29.7.0"
  ],
  "symbols": [
    "matcherHint",
    "printExpected",
    "printReceived",
    "printWithType",
    "diff",
    "stringify",
    "matcherErrorMessage",
    "ensureActualIsNumber",
    "ensureExpectedIsNumber",
    "ensureNoExpected",
    "pluralize",
    "getLabelPrinter"
  ],
  "constraints": {
    "executionContext": "node"
  },
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    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
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}

'use strict';

const {
  matcherHint,
  printExpected,
  printReceived,
  printWithType,
  diff,
  stringify,
  matcherErrorMessage,
  ensureActualIsNumber,
  ensureExpectedIsNumber,
  ensureNoExpected,
  pluralize,
  getLabelPrinter
} = require('jest-matcher-utils');

/**
 * Formats standard matcher header string.
 * @param {string} matcherName
 * @param {string} [received]
 * @param {string} [expected]
 * @param {object} [options]
 * @returns {string}
 */
function formatMatcherHint(matcherName, received, expected, options) {
  return matcherHint(matcherName, received, expected, options);
}

/**
 * Formats expected value for display.
 * @param {*} value
 * @returns {string}
 */
function formatExpected(value) {
  return printExpected(value);
}

/**
 * Formats received value for display.
 * @param {*} value
 * @returns {string}
 */
function formatReceived(value) {
  return printReceived(value);
}

/**
 * Computes difference between expected and received.
 * @param {*} expected
 * @param {*} received
 * @param {object} [options]
 * @returns {string|null}
 */
function computeDiff(expected, received, options) {
  return diff(expected, received, options);
}

module.exports = {
  matcherHint,
  printExpected,
  printReceived,
  printWithType,
  diff,
  stringify,
  matcherErrorMessage,
  ensureActualIsNumber,
  ensureExpectedIsNumber,
  ensureNoExpected,
  pluralize,
  getLabelPrinter,
  formatMatcherHint,
  formatExpected,
  formatReceived,
  computeDiff
};

'use strict';

const assert = require('assert');
const {
  matcherHint,
  printExpected,
  printReceived,
  printWithType,
  diff,
  stringify,
  matcherErrorMessage,
  ensureActualIsNumber,
  ensureExpectedIsNumber,
  ensureNoExpected,
  pluralize,
  getLabelPrinter,
  formatMatcherHint,
  formatExpected,
  formatReceived,
  computeDiff
} = require('../src/index.js');

// 1. matcherHint formats standard matcher invocation headers with expected and received labels
{
  const hint = matcherHint('toBe', 'received', 'expected');
  assert.strictEqual(hint, 'expect(received).toBe(expected)');

  const customHint = formatMatcherHint('toEqual', 'actual', 'expected');
  assert.strictEqual(customHint, 'expect(actual).toEqual(expected)');
}

// 2. matcherHint supports options including isNot, promise, and comment modifiers
{
  const hintNot = matcherHint('toBe', undefined, undefined, { isNot: true });
  assert.strictEqual(hintNot, 'expect(received).not.toBe(expected)');

  const hintRejects = matcherHint('toThrow', undefined, undefined, { promise: 'rejects' });
  assert.strictEqual(hintRejects, 'expect(received).rejects.toThrow(expected)');

  const hintWithComment = matcherHint('toBe', 'received', 'expected', { comment: 'equality check' });
  assert.strictEqual(hintWithComment, 'expect(received).toBe(expected) // equality check');
}

// 3. printExpected formats expected values with quotes and syntax formatting
{
  const printedNum = formatExpected(123);
  assert.strictEqual(printedNum, '123');

  const printedStr = printExpected('hello');
  assert.strictEqual(printedStr, '"hello"');

  const printedArr = printExpected([1, 2]);
  assert.strictEqual(printedArr, '[1, 2]');
}

// 4. printReceived formats received values with quotes and syntax formatting
{
  const printedNum = formatReceived(456);
  assert.strictEqual(printedNum, '456');

  const printedStr = printReceived('world');
  assert.strictEqual(printedStr, '"world"');

  const printedObj = printReceived({ key: 'val' });
  assert.strictEqual(printedObj, '{"key": "val"}');
}

// 5. printWithType displays the type and formatted value of an argument
{
  const formatted = printWithType('received', 'abc', printReceived);
  assert.strictEqual(formatted, 'received has type:  string\nreceived has value: "abc"');

  const formattedNum = printWithType('expected', 99, printExpected);
  assert.strictEqual(formattedNum, 'expected has type:  number\nexpected has value: 99');
}

// 6. diff computes and returns a unified string diff between expected and received values
{
  const diffResult = computeDiff('hello world', 'hello there');
  assert.ok(typeof diffResult === 'string');
  assert.ok(diffResult.includes('- Expected'));
  assert.ok(diffResult.includes('+ Received'));

  const noDiff = diff('same', 'same');
  assert.ok(noDiff.includes('Compared values have no visual difference'));
}

// 7. stringify serializes JavaScript values cleanly into string representation
{
  assert.strictEqual(stringify(null), 'null');
  assert.strictEqual(stringify(undefined), 'undefined');
  assert.strictEqual(stringify(true), 'true');
  assert.strictEqual(stringify(100), '100');
  assert.strictEqual(stringify('test'), '"test"');
  assert.strictEqual(stringify({ a: 1 }), '{"a": 1}');
  assert.strictEqual(stringify([1, 2]), '[1, 2]');
}

// 8. matcherErrorMessage formats standard matcher failure messages with hints and explanations
{
  const hint = matcherHint('toBeGreaterThan');
  const explanation = 'expected value must be a number or bigint';
  const printedType = printWithType('Expected', 'string-val', printExpected);
  const message = matcherErrorMessage(hint, explanation, printedType);

  assert.ok(message.includes('expect(received).toBeGreaterThan(expected)'));
  assert.ok(message.includes('Matcher error: expected value must be a number or bigint'));
  assert.ok(message.includes('Expected has type:  string'));
}

// 9. ensureActualIsNumber validates received value is numeric and throws formatted error otherwise
{
  assert.doesNotThrow(() => ensureActualIsNumber(42, 'toBeCloseTo'));
  assert.doesNotThrow(() => ensureActualIsNumber(42n, 'toBeCloseTo'));

  assert.throws(
    () => ensureActualIsNumber('invalid', 'toBeCloseTo'),
    (err) => {
      assert.ok(err instanceof Error);
      assert.ok(err.message.includes('received value must be a number or bigint'));
      return true;
    }
  );
}

// 10. ensureExpectedIsNumber validates expected value is numeric and throws formatted error otherwise
{
  assert.doesNotThrow(() => ensureExpectedIsNumber(100, 'toBeCloseTo'));
  assert.doesNotThrow(() => ensureExpectedIsNumber(100n, 'toBeCloseTo'));

  assert.throws(
    () => ensureExpectedIsNumber('invalid', 'toBeCloseTo'),
    (err) => {
      assert.ok(err instanceof Error);
      assert.ok(err.message.includes('expected value must be a number or bigint'));
      return true;
    }
  );
}

// 11. ensureNoExpected verifies matcher does not receive an expected argument
{
  assert.doesNotThrow(() => ensureNoExpected(undefined, 'toBeNull'));

  assert.throws(
    () => ensureNoExpected('extra-arg', 'toBeNull'),
    (err) => {
      assert.ok(err instanceof Error);
      assert.ok(err.message.includes('this matcher must not have an expected argument'));
      return true;
    }
  );
}

// 12. pluralize formats countable noun singular and plural forms based on count
{
  assert.strictEqual(pluralize('apple', 0), 'zero apples');
  assert.strictEqual(pluralize('apple', 1), 'one apple');
  assert.strictEqual(pluralize('apple', 2), 'two apples');
  assert.strictEqual(pluralize('apple', 14), '14 apples');
}

// 13. getLabelPrinter creates formatted and aligned label printers for matcher outputs
{
  const printLabel = getLabelPrinter('Expected', 'Received value');
  assert.strictEqual(printLabel('Expected'), 'Expected:       ');
  assert.strictEqual(printLabel('Received value'), 'Received value: ');
}

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