Acceptance test–driven development

Acceptance test–driven development (ATDD) is a development methodology based on communication between the business customers, the developers, and the testers. ATDD encompasses many of the same practices as specification by example,behavior-driven development (BDD), example-driven development (EDD), and support-driven development also called story test–driven development (SDD). All these processes aid developers and testers in understanding the customer's needs prior to implementation and allow customers to be able to converse in their own domain language.

ATDD is closely related to test-driven development (TDD). It differs by the emphasis on developer-tester-business customer collaboration. ATDD encompasses acceptance testing, but highlights writing acceptance tests before developers begin coding.

Acceptance tests are from the user's point of view – the external view of the system. They examine externally visible effects, such as specifying the correct output of a system given a particular input. Acceptance tests can verify how the state of something changes, such as an order that goes from "paid" to "shipped". They also can check the interactions with interfaces of other systems, such as shared databases or web services. In general, they are implementation independent, although automation of them may not be.

Acceptance tests are created when the requirements are analyzed and prior to coding. They can be developed collaboratively by requirement requester (product owner, business analyst, customer representative, etc.), developer, and tester. Developers implement the system using the acceptance tests. Failing tests provide quick feedback that the requirements are not being met. The tests are specified in business domain terms. The terms then form a ubiquitous language that is shared between the customers, developers, and testers. Tests and requirements are interrelated. A requirement that lacks a test may not be implemented properly. A test that does not refer to a requirement is an unneeded test. An acceptance test that is developed after implementation begins represents a new requirement.

Acceptance tests are a part of an overall testing strategy. They are the customer tests that demonstrate the business intent of a system. Component tests are technical acceptance tests developed by an architect that specify the behavior of large modules. Unit tests are created by the developer to drive easy-to-maintain code. They are often derived from acceptance tests and unit tests. Cross-functional testing includes usability testing, exploratory testing, and property testing (scaling and security).

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