Impact of software testability considerations on software development life cycle

The testability of software has been defined as provisions that can be made in the software during the design and coding phases, so that test-plans can be executed easily and systematically. Software testability measures are defined in terms of controllability and observability measures. Observability measures are incorporated in the software to facilitate observation of internal states. Controllability measures are incorporated to allow the software to attain states required for execution of various tests, which are normally difficult to achieve through user interface commands. Specificity of testability measures to be incorporated in software depends upon the test-plan. Hence, the test-plan, for each pre-testing phase of software development, is an essential input for the next phase to make the software testable. The design verification test-plan also has to be checked for testability, and, if required, the design has to be revised to incorporate necessary testability measures. A similar process has to be repeated with a detail design verification test-plan as well as a code verification test-plan. The impact of software testability considerations has resulted in the 'Testable-Software Development Model'.