Testing Patterns Skill

Help write clear, maintainable, effective tests.

Test Structure (AAA Pattern)

// Arrange - Set up test data and conditions
// Act - Execute the code under test
// Assert - Verify the expected outcome

Naming Convention

test_[unit]_[scenario]_[expected result]

Examples:
- test_calculateTotal_withEmptyCart_returnsZero
- test_login_withInvalidPassword_throwsAuthError
- test_fetchUser_whenNotFound_returns404

What to Test

Unit Tests

• Pure functions and calculations
• Business logic
• Edge cases and boundaries
• Error conditions

Integration Tests

• API endpoints
• Database operations
• External service interactions
• Authentication flows

Do NOT Test

• Framework/library internals
• Private methods directly
• Trivial getters/setters
• Third-party code

Test Quality Checklist

• Tests one thing only
• Clear test name describes behavior
• Independent (no test order dependency)
• Fast (mock external dependencies)
• Deterministic (no flaky tests)
• Readable (future you is the audience)

Mocking Guidelines

Mock:

• External APIs
• Database (for unit tests)
• Time/dates
• Random values
• File system (when appropriate)

Don't mock:

• The thing you're testing
• Simple value objects
• Everything (leads to brittle tests)

Coverage Strategy

Focus on:

• Critical business logic: 90%+
• Happy paths: 100%
• Error paths: 80%+
• Edge cases: Case by case

Avoid:

• Chasing 100% blindly
• Testing implementation details
• Duplicate coverage