What is Test-Driven Development.

TDD is a programming paradigm where tests are written to drive the development of the application.

It is mainly aimed at writing clean code that works.

The Red-Green-Refactor Principle

This principle is a practical approach on how to implement TDD.

The diagram illustrates the three principles of TDD:

1. Write a test and see it fail.
2. Write just enough code to make the test pass.
3. Refactor the code if any code smells are detected.

This principle is easy to follow at first but the downside with it is that it does not help a beginner understand how to get started writing tests.

Types of TDD

TDD is a mixed concept with different variations and approaches.

1. Unit Test Driven-Development(UTDD)
2. Behavior-Driven Development (BDD)
3. Acceptance Test-Driven Development(ATDD)

ATDD

ATDD describes the behavior of a software from a user's point of view by focusing on the business value of the application and not the implementation details.

ATDD and UTDD can always be combined in one diagram as indicated below.

The diagram above describes the following steps followed during ATDD:

1. Write an acceptance test and see it fail.
2. Write a unit test and see it fail.
3. Write code to make the unit test pass.
4. Refactor the code.
5. Repeat steps 2 - 4 unit all the acceptance tests passes.

BDD

Behavior-Driven Development is an agile practice that encourages collaboration among different roles, developers, quality engineers, business analysts, or even other interested parties in a software project.

Although BDD is to some extent a general idea about how software development should be managed by both business interests and technical insight, the practice of BDD involves some specialized tools.

For example, domain-specific language (DSL) is used to write tests in natural language that can be easily understood by nontechnical people and can be interpreted by code and executed behind the scenes.

Prerequisites of TDD

One major prerequisite for a developer who is getting into TDD is the ability to detect code smells and how to refactor them into a good design.