Test Driven Design

TDD is a software development methodology where you write tests before you write the actual code. The process can be summarized in three primary steps:

• Red: Write a failing test.
• Green: Write the minimum code to make the test pass.
• Refactor: Refine the written code while ensuring that the test still passes.

Simple example of TDD using PHP

The Requirement

Suppose you need to write a function that adds two numbers.