TDD, BDD and ATDD were introduced by XP Extreme Programming is an agile software development framework. They are unit testing approaches. TDD, BDD and ATDD are a software development technique which uses unit tests to incrementally deliver small pieces of functionality. TDD is a developer focused process. In Test Driven Development TDD , first come tests and then the code. The minimal piece of code is written in order to pass the designed test. In other words, it is the process of testing the code before its accrual writing. If the code passes the test, then developers can proceed to its refactoring. Behavior Driven Development BDD is a customer focused process. It is based on the full and clear understanding of the system or module behavior but in the terms of business client. The tests for TDD are created by developers for developers. The test for BDD can be written by testers or technical managers. Acceptance Test Driven Development ATDD is towards the developer focused side of things. ATDD is a technique where the entire team collaborates to define the acceptance criteria of a story before the implementation actually begins. These acceptance tests are supported necessary information. Using the Given When Then format, ATDD approach can implement. Myint Myint Moe "Comparative Study of Test-Driven Development (TDD), Behavior-Driven Development (BDD) and Acceptance Test-Driven Development (ATDD)" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-4 , June 2019, URL: https://www.ijtsrd.com/papers/ijtsrd23698.pdf