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Testing Modern JavaScript Syntax Integration in Create-React-App

This comprehensive integration test suite validates modern JavaScript language features and syntax support in Create React App. It systematically tests ES6+ functionality through DOM manipulation and element verification, ensuring compatibility across different JavaScript syntax patterns.

Test Coverage Overview

The test suite provides extensive coverage of ES6+ language features including:

Array operations (destructuring, spread)
Async programming (async/await, promises)
Class features (properties, computed properties)
Object manipulation (destructuring, spread)
Modern syntax (template interpolation, default parameters, rest parameters)

Implementation Analysis

Tests utilize Jest’s async/await pattern for DOM testing, with each test case following a consistent structure of initializing DOM elements and verifying child element counts. The implementation leverages custom DOM initialization through the initDOM helper, ensuring isolated testing environments for each syntax feature.

Technical Details

Key technical components include:

Jest test framework for async testing
Custom initDOM utility for DOM manipulation
Element count verification (consistently checking for 4 child elements)
Proper cleanup through afterEach hooks
DOM window management for memory efficiency

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Isolated test cases with proper cleanup
Consistent test structure and assertions
Proper async/await handling
Modular test organization by feature
Clear test case naming and categorization

facebook/create-react-app

packages/react-scripts/fixtures/kitchensink/template/integration/syntax.test.js

            
/**
 * Copyright (c) 2015-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

import initDOM from './initDOM';

describe('Integration', () => {
  describe('Language syntax', () => {
    let doc;

    afterEach(() => {
      doc && doc.defaultView.close();
      doc = undefined;
    });

    it('array destructuring', async () => {
      doc = await initDOM('array-destructuring');

      expect(
        doc.getElementById('feature-array-destructuring').childElementCount
      ).toBe(4);
    });

    it('array spread', async () => {
      doc = await initDOM('array-spread');

      expect(doc.getElementById('feature-array-spread').childElementCount).toBe(
        4
      );
    });

    it('async/await', async () => {
      doc = await initDOM('async-await');

      expect(doc.getElementById('feature-async-await').childElementCount).toBe(
        4
      );
    });

    it('class properties', async () => {
      doc = await initDOM('class-properties');

      expect(
        doc.getElementById('feature-class-properties').childElementCount
      ).toBe(4);
    });

    it('computed properties', async () => {
      doc = await initDOM('computed-properties');

      expect(
        doc.getElementById('feature-computed-properties').childElementCount
      ).toBe(4);
    });

    it('custom interpolation', async () => {
      doc = await initDOM('custom-interpolation');

      expect(
        doc.getElementById('feature-custom-interpolation').childElementCount
      ).toBe(4);
    });

    it('default parameters', async () => {
      doc = await initDOM('default-parameters');

      expect(
        doc.getElementById('feature-default-parameters').childElementCount
      ).toBe(4);
    });

    it('destructuring and await', async () => {
      doc = await initDOM('destructuring-and-await');

      expect(
        doc.getElementById('feature-destructuring-and-await').childElementCount
      ).toBe(4);
    });

    it('generators', async () => {
      doc = await initDOM('generators');

      expect(doc.getElementById('feature-generators').childElementCount).toBe(
        4
      );
    });

    it('object destructuring', async () => {
      doc = await initDOM('object-destructuring');

      expect(
        doc.getElementById('feature-object-destructuring').childElementCount
      ).toBe(4);
    });

    it('object spread', async () => {
      doc = await initDOM('object-spread');

      expect(
        doc.getElementById('feature-object-spread').childElementCount
      ).toBe(4);
    });

    it('promises', async () => {
      doc = await initDOM('promises');

      expect(doc.getElementById('feature-promises').childElementCount).toBe(4);
    });

    it('rest + default', async () => {
      doc = await initDOM('rest-and-default');

      expect(
        doc.getElementById('feature-rest-and-default').childElementCount
      ).toBe(4);
    });

    it('rest parameters', async () => {
      doc = await initDOM('rest-parameters');

      expect(
        doc.getElementById('feature-rest-parameters').childElementCount
      ).toBe(4);
    });

    it('template interpolation', async () => {
      doc = await initDOM('template-interpolation');

      expect(
        doc.getElementById('feature-template-interpolation').childElementCount
      ).toBe(4);
    });
  });
});