Unit Test

Skill: Unit Testing (Cross-Cutting)

Purpose

This skill is used to create unit tests for code components. Unit tests verify that individual functions, methods, or classes work correctly in isolation.

When to Use

• When testing individual functions or methods
• When testing class methods in isolation
• When testing utility functions
• When testing business logic
• When testing data transformations
• When ensuring code correctness before integration

Step-by-Step Process

Step 1: Identify Test Targets

• Analyze the code to identify testable units
• List all public methods/functions
• Identify edge cases and boundary conditions
• Determine expected inputs and outputs

Step 2: Set Up Test Framework

• Choose appropriate testing framework (Jest, PHPUnit, pytest, etc.)
• Configure test environment
• Set up test structure matching project conventions
• Ensure test framework is installed and configured

Step 3: Write Test Cases

• Create test file matching source file structure
• Write tests for each function/method
• Test normal cases (happy path)
• Test edge cases (null, empty, boundary values)
• Test error cases (invalid input, exceptions)
• Use descriptive test names

Step 4: Run and Verify

• Run tests to ensure they pass
• Check test coverage if available
• Refactor if needed
• Ensure tests are fast and isolated

Step 5: Document Test Cases

• Add comments for complex test scenarios
• Document test data and expected outcomes
• Update test documentation if needed

Required Input

• Source code: Code to be tested (functions, methods, classes)
• Test framework: Testing framework to use (Jest, PHPUnit, pytest, etc.)
• Project structure: Understanding of where tests should be placed
• Dependencies: List of dependencies that need to be mocked

Expected Output

• Complete unit test files
• Tests covering normal, edge, and error cases
• Test assertions verifying expected behavior
• Test data and fixtures if needed
• Passing test suite

Tone & Rules

Test Naming

• Use descriptive names: test_user_registration_with_valid_email()
• Follow pattern: test_<what>_<condition>_<expected_result>
• Use clear, readable test names

Test Structure

• Arrange: Set up test data and dependencies
• Act: Execute the code being tested
• Assert: Verify the results
• Clean up: Reset state if needed

Coverage Goals

• Aim for high coverage of critical paths
• Test all public methods
• Test edge cases and error handling
• Don't test implementation details

Limitations

• ❌ DO NOT test private methods directly (test through public interface)
• ❌ DO NOT write tests that depend on other tests
• ❌ DO NOT test external dependencies (use mocks)
• ❌ DO NOT write slow tests (use mocks for I/O)
• ❌ DO NOT test framework code

Available Templates

• templates/unit-test-template.js - JavaScript/Jest template
• templates/unit-test-template.php - PHP/PHPUnit template
• templates/unit-test-template.py - Python/pytest template

Available Scripts

• scripts/generate-test-stubs.sh - Generate test file stubs from source code

Examples

See examples/ directory for reference:

• good-unit-test/ - Well-structured unit tests
• bad-unit-test/ - Examples to avoid

Links to Other Skills

• integration-test: Use after unit tests for integration testing
• e2e-test: Use for end-to-end testing
• documents: Use to document test strategy