Over the years I have come to describe Test Driven Development in terms of three simple rules. They are:
- You are not allowed to write any production code unless it is to make a failing unit test pass.
- You are not allowed to write any more of a unit test than is sufficient to fail; and compilation failures are failures.
- You are not allowed to write any more production code than is sufficient to pass the one failing unit test.
You have to think about it, but it makes sense. TDD is not always required but it is always advised, even if you don't use it in your day-to-day work you should at least understand how it works and try it a few times/examples.