Test-Driven Development

Understand the TDD mindset: why writing tests before implementation produces better design, fewer bugs, and more maintainable code than testing after the fact.

Execute the Red-Green-Refactor cycle with precision: write the minimal failing test, implement just enough to pass, then refactor aggressively while keeping tests green.

Learn how to choose the right first test for any TDD session: the simplest degenerate case, triangulation to drive generalisation, and the test list technique for planning a session.

Refactor production code safely using Martin Fowler's catalogue of behaviour-preserving transformations, with tests as your safety net and IDE automation to reduce risk.

Apply the complete Red-Green-Refactor cycle to pure functions, utility classes, and data transformation logic — the bread and butter of backend TDD in TypeScript.

Apply Red-Green-Refactor to React components using React Testing Library: write component tests before JSX exists, drive props and state through failing tests, and TDD custom hooks.

Understand the two major TDD strategies: outside-in (London school) starts from acceptance tests and works inward, while inside-out (Chicago school) builds from the bottom up. Learn when each approach is appropriate.

Apply TDD to build a real NestJS REST endpoint end-to-end: start from a failing Supertest acceptance test, work inward through controller and service layers, and finish with full test coverage.

Keep your test suite healthy over time: refactor tests alongside production code, eliminate test duplication, fix brittle tests before they become ignored, and establish team practices that prevent quality regression.

Apply Behavior-Driven Development to bridge business requirements and executable tests using Given-When-Then scenarios, and use BDD thinking to write better TDD tests.