Testing Patterns

Core Principle

Test behavior, not implementation. 100% coverage through business behavior, not implementation details.

Example: Validation code in payment-validator.ts gets 100% coverage by testing processPayment() behavior, NOT by directly testing validator functions.

Test Through Public API Only

Never test implementation details. Test behavior through public APIs.

Why this matters:

• Tests remain valid when refactoring
• Tests document intended behavior
• Tests catch real bugs, not implementation changes