This ebook is an attempt to create open-source extensive tutorial on Test-Driven Development (TDD). I’m writing this book because I’m an enthusiast of Test-Driven Development (TDD). I believe that TDD is a major improvement over other software development methodologies that I have used to deliver quality software. I also believe that this is true not only for me, but for many other software developers. This raises the question: why don’t more people learn and use TDD as their software delivery method of choice? In my professional life, I haven’t seen the adoption rate to be high enough to justify the claim that TDD is now mainstream. The language of choice for code examples is C#, however, I made some exception from the typical C# code conventions.