Behaviour Driven Development (BDD) is a synthesis and refinement of practices stemming from Test Driven Development (TDD) and Acceptance Test-Driven Development (ATDD). BDD augments TDD and ATDD byapplying the “Five Why’s” principle to each proposed user story so that its purpose is clearly related to business outcomes. Five Why's is an iterative interrogative approach for uncovering the cause-and-effect links at the root of a problem. The main purpose of this technique is to uncover the core cause of a flaw or problem by asking "Why?" repeatedly. Each response serves as the foundation for the next question.