Learn how Value Objects and Entities make invalid states impossible in TypeScript. Build self-validating domain code with TDD — the blocks that can't break.

Every chess database begins with the same question: how do we store a game? PGN is the default answer — human-readable, portable, and surprisingly wasteful. A walkthrough of moving toward binary coordinates and legal-move indexing, and the engineering trade-off between the smallest format and the fastest one.

Learn why test-driven development is really about permission to refactor, not catching bugs. With TypeScript examples, Result<T, E> patterns, and behavior-based testing from 3 years in production.