Testing Test Writing

Unit tests for critical paths prioritize core business logic over edge cases. Write tests covering valid inputs and typical scenarios—like password validation in a login flow—using descriptive names and standard file patterns (*.test.ts, *.spec.js). This maintains development velocity while ensuring essential functionality works.

Unit tests validate individual functions in isolation; integration tests verify components work together (e.g., user authentication with database); end-to-end tests cover complete user workflows. For a login feature, use all three: unit for password hashing, integration for database queries, end-to-end for the full login success scenario.

Mocking replaces real services with controlled substitutes, ensuring tests run fast and in isolation. Replace database calls, API requests, and third-party services with mock implementations that return predictable responses, letting you test your code without external dependencies.

Behavior-driven tests validate what users observe—login succeeds, price calculates correctly—rather than how internals work. This makes tests resilient to refactoring; you can change implementation without rewriting tests, reducing maintenance burden while keeping coverage effective.

Strategic testing aligns with TDD by writing tests for critical workflows first, deferring edge cases to dedicated phases. This approach maintains development speed and code reliability without over-engineering, focusing test effort on core business paths that matter most.

Use standard patterns: *.test.ts, *.spec.js, or __tests__/* directories. Organize tests alongside source files or in a dedicated test folder. Descriptive test names clarify what behavior they validate, making test suites easier to navigate and maintain across unit, integration, and end-to-end layers.