TDD, how to develop by testing

Test Driven Development (TDD) is an evolutionary approach to development which combines test-first development where you write a test before you write just enough production code to fulfill that test and refactoring.

Steps?

The first step is to quickly add a test, basically just enough code to fail.  Next you run your tests, often the complete test suite although for sake of speed you may decide to run only a subset, to ensure that the new test does in fact fail. You then update your functional code to make it pass the new tests. The fourth step is to run your tests again. If they fail you need to update your functional code and retest. Once the tests pass the next step is to start over.

TDD completely turns traditional development around. When you first go to implement a new feature, the first question that you ask is whether the existing design is the best design possible that enables you to implement that functionality.

There are two levels of TDD:

1. Acceptance TDD (ATDD).  With ATDD you write a single acceptance test, or behavioral specification depending on your preferred terminology, and then just enough production functionality/code to fulfill that test. The goal of ATDD is to specify detailed, executable requirements for your solution on a just in time (JIT) basis. ATDD is also called Behavior Driven Development (BDD).
2. Developer TDD. With developer TDD you write a single developer test, sometimes inaccurately referred to as a unit test, and then just enough production code to fulfill that test. The goal of developer TDD is to specify a detailed, executable design for your solution on a JIT basis. Developer TDD is often simply called TDD.

Why using TDD?

A significant advantage of TDD is that it enables you to take small steps when writing software. This is a practice that I have promoted for years because it is far more productive than attempting to code in large steps.

To learn more visit Agile Data Page: Introduction to Test Driven Development (TDD) or watch the next video.

-RC