Imagine you are in an interview. You are at the stage where the interviewer has failed to notice the gaps in your CV and is actually forced to ask you some questions. Not having prepared, their expression drains they are forced to think up one on the spot. They can only come up with...
"What are the stages in developing software?".
Pah, easy!
"Design, Code, Test and Debug."
A quick handshake later and you know you are in the running. You also know that in the rush of a real project, no one actually does this stuff, but that's the correct answer and you've got to play the game after all. Didn't even have to think about that one.

Suppose we did think about it.

Not just made a cursory effort to do it, but actually examine if it is really the right thing to do. Some people have done exactly this and one of those people is Kent Beck. Kent Beck is co-founder, along with Ward Cunningham, of eXtreme Programming. His latest manifesto, "Test Driven Development", is a further distillation of the coding practices of XP. Like most of Kent's writings, this book is direct and controversal. Like most of Kent's ideas, it's based on front line experience, is simple and it works.

You start by writing a test.