---

name: cui-javascript-unit-testing description: Jest unit testing standards covering configuration, test structure, testing patterns, and coverage requirements allowed-tools:

• Read
• Grep
• Glob

---

JavaScript Unit Testing Standards

REFERENCE MODE: This skill provides reference material. Load specific standards on-demand based on current task.

Overview

This skill provides comprehensive Jest unit testing standards for CUI JavaScript projects, covering Jest configuration, test organization, component testing patterns, mocking strategies, and coverage requirements.

Prerequisites

To effectively use this skill, you should have:

• JavaScript testing experience with Jest framework
• Understanding of unit testing principles (AAA pattern, test isolation)
• Familiarity with DOM testing and component testing concepts
• Knowledge of mocking and test doubles

Standards Documents

This skill includes the following standards documents:

• jest-configuration.md - Jest setup, package.json config, transform patterns, module mapping
• test-structure.md - Test file organization, naming conventions, setup files, directory structure
• testing-patterns.md - Component testing, mocking strategies, assertions, AAA pattern
• coverage-standards.md - Coverage thresholds (80%), reporting formats, collection strategies

What This Skill Provides

Jest Configuration

• Core Setup: Jest environment configuration (jsdom), testMatch patterns
• Module Mapping: Mock configuration for Lit, DevUI, and other dependencies
• Transform Configuration: Babel-jest setup for ES modules, transformIgnorePatterns
• Setup Files: Global test setup, DOM polyfills, mock implementations

Test Structure

• File Organization: Standard directory structure (components/, mocks/, setup/, utils/)
• Naming Conventions: Component tests (*.test.js), integration tests, utility tests
• Setup Files: jest.setup.js, jest.setup-dom.js configuration patterns
• Test File Structure: Describe blocks, beforeEach/afterEach patterns

Testing Patterns

• Component Testing: Lit component test structure, rendering tests, property tests
• Mocking Strategies: Lit framework mocks, DevUI mocks, external dependency mocking
• Assertion Patterns: Jest matchers, @testing-library/jest-dom assertions
• AAA Pattern: Arrange-Act-Assert structure, test isolation principles

Coverage Standards

• Minimum Thresholds: 80% for branches, functions, lines, statements
• Coverage Collection: Strategies for mocked vs actual source files
• Reporting Formats: text, lcov, html, cobertura for different use cases
• Coverage Directory: target/coverage integration with build system

When to Activate

This skill should be activated when:

1. Writing Tests: Creating new Jest unit tests for JavaScript code
2. Configuring Jest: Setting up Jest for a new project or updating configuration
3. Test Review: Reviewing test quality and coverage compliance
4. Mocking: Implementing mocks for Lit components or external dependencies
5. Coverage Analysis: Understanding or improving test coverage
6. Test Structure: Organizing test files and setup
7. CI/CD Integration: Configuring test execution in build pipelines

Workflow

When this skill is activated:

1. Understand Context

• Identify the specific testing task or requirement
• Determine which standards documents are most relevant
• Check existing project Jest configuration

2. Apply Standards

• Reference appropriate standards documents for guidance
• Follow Jest configuration patterns from jest-configuration.md
• Organize test files according to test-structure.md
• Apply testing patterns from testing-patterns.md
• Ensure coverage meets thresholds from coverage-standards.md

3. Quality Assurance

• Run tests to verify they execute correctly
• Check coverage reports meet 80% thresholds
• Verify mocks are properly configured
• Ensure tests are isolated and independent
• Validate test naming and organization

4. Documentation

• Document complex mocking strategies with clear comments
• Explain non-obvious test setup or configuration
• Note any project-specific test patterns
• Update README if adding new test utilities

Tool Access

This skill provides access to Jest testing standards through:

• Read tool for accessing standards documents
• Standards documents use Markdown format for compatibility
• All standards are self-contained within this skill
• Cross-references between standards use relative paths

Integration Notes

Related Skills

For comprehensive JavaScript development, this skill works with:

• cui-javascript skill - Core JavaScript patterns and code quality
• cui-css skill - CSS testing patterns (if applicable)
• Other testing skills (E2E testing to be provided in separate skill)

Build Integration

Jest testing integrates with:

• npm for package management and test execution
• Maven frontend-maven-plugin for build automation
• Jest CLI for test execution and coverage reporting
• Babel for ES module transformation

Quality Tools

Test quality is enforced through:

• Jest framework for test execution
• @testing-library/jest-dom for enhanced DOM assertions
• Coverage reports for quality gates
• ESLint jest plugin for test code quality

Best Practices

When writing Jest tests in CUI projects:

1. Meet coverage thresholds - 80% minimum for all metrics
2. Use jsdom environment for DOM and component testing
3. Mock external dependencies - Lit, DevUI, and other frameworks
4. Follow AAA pattern - Arrange, Act, Assert for clarity
5. Keep tests isolated - Independent, no shared state
6. Organize logically - Group related tests with describe blocks
7. Use descriptive names - Test names explain expected behavior
8. Setup properly - Use jest.setup.js and jest.setup-dom.js for global config

Workflows

Workflow: Analyze Coverage

Analyzes existing test coverage reports (Jest/Istanbul JSON or LCOV format) and returns structured coverage data.

When to use: After running tests with coverage to identify low-coverage areas and uncovered code.

Steps:

1. Locate coverage report

   • Look for coverage/coverage-summary.json (JSON format - preferred)
   • Or coverage/lcov.info (LCOV format - more detailed)

2. Run coverage analysis script

   Script: pm-dev-frontend:cui-javascript-unit-testing → js-coverage.py

   python3 .plan/execute-script.py pm-dev-frontend:cui-javascript-unit-testing:js-coverage analyze --report coverage/coverage-summary.json
   # Or for LCOV format:
   python3 .plan/execute-script.py pm-dev-frontend:cui-javascript-unit-testing:js-coverage analyze --report coverage/lcov.info --format lcov
   # With custom threshold:
   python3 .plan/execute-script.py pm-dev-frontend:cui-javascript-unit-testing:js-coverage analyze --report coverage/coverage-summary.json --threshold 80
   

3. Process results

   • Review overall_coverage metrics (lines, statements, functions, branches)
   • Identify files in low_coverage_files array (below threshold)
   • Note files with CRITICAL severity (< 50% coverage)
   • Check uncovered_lines for specific areas needing tests

JSON Output Contract:

{
  "status": "success",
  "data": {
    "report_format": "JSON",
    "overall_coverage": {
      "line_coverage": 85.5,
      "statement_coverage": 84.8,
      "function_coverage": 90.1,
      "branch_coverage": 78.2
    },
    "by_file": [...],
    "low_coverage_files": [
      {"file": "src/utils.js", "coverage": 45.2, "severity": "CRITICAL", "uncovered_lines": [12, 34]}
    ]
  },
  "metrics": {
    "total_files": 45,
    "files_with_good_coverage": 38,
    "files_with_low_coverage": 7,
    "threshold": 80
  }
}

Error handling:

• Script returns status: "error" if report not found
• Supported formats: JSON (coverage-summary.json), LCOV (lcov.info)