This document provides a guided walkthrough of implementing the FizzBuzz kata using test-driven development (TDD) principles in C# with NUnit. It begins with high-level reminders of TDD and simple design. It then demonstrates incrementally writing tests and code, refactoring along the way, to arrive at a final implementation that uses functions and rules to determine the FizzBuzz translation in a modular way. It also shows how to modify the rules to implement a different translation as an example of flexibility.