This document discusses test driven development (TDD) and its introduction. It was popularized by extreme programming (XP) as a "testing strategy" in the first edition and "test-first" in the second edition. The document discusses that TDD is not just about testing, but also helps produce unambiguous requirements, improved software design, loose coupling, and increased productivity. It reviews best practices shown in a demo, such as using NUnit assertions and the red-green-refactor process. It concludes with additional discussion points around TDD pragmatism versus religion, continuous integration, testing challenges, and recommended agile reading.