Acceptance Test

It is one thing to write user stories. To ensure that a system behaves as it should, the customer specifies acceptance tests. If these acceptance test are passed successfully, the user story has been implemented correctly.

The very same acceptance tests are used by the programmers for checking whether - from their point of view- they have implemented the user story correctly, e.g. whether they have to implement additional tasks.

Example of an acceptance test: "The system knows the customer numbers 245, 746, and 342. After entering one of these numbers the order will be accepted by the system. Upon entering a number different from the mentioned ones, the screen for adding a new customer to the system will be displayed."

Acceptance tests do not loose their value, even after the customer has approved the successful implementation of the user story. The user stories are useful for ensuring that subsequent changes of the system does not affect already existing functionality. The acceptance tests take on the role of regression tests.

In addition to the acceptance tests the programmer uses unit tests for testing parts of the system, e.g. the methods of a class.