It should be permanently tested during the development. For example, testing should be done during the night. In addition, there is the developer approach of Test Driven Development. A test for a function is described then the development of the code is completed. After the development it can be understood whether the test worked and changes are to be accomplished. It should also be tried to keep the code coverage as large as possible. A user acceptance test enables a testing of the software with the customer so that a high satisfaction with the customer can be produced.