Test Design

Test Design
Thus far, the tester has produced a lot of analytical output, some semi-formalized documentary artifacts, and several tentative approaches to testing the software. At this point, the tester is ready for the next step: test design.
The right wing of the butterfly represents the act of designing and implementing the test cases needed to verify the design artifact as replicated in the implementation. Like test analysis, it is a relatively large piece of work. Unlike test analysis, however, the focus of test design is not to assimilate information created by others, but rather to implement procedures, techniques, and data sets that achieve the test’s objective(s).
The outputs of the test analysis phase are the foundation for test design. Each requirement or design construct has had at least one technique (a measurement, demonstration, or analysis) identified during test analysis that will validate or verify that requirement. The tester must now put on his or her development hat and implement the intended technique.
Software test design, as a discipline, is an exercise in the prevention, detection, and elimination of bugs in software. Preventing bugs is the primary goal of software testing [BEIZ90]. Diligent and competent test design prevents bugs from ever reaching the implementation stage. Test design, with its attendant test analysis foundation, is therefore the premiere weapon in the arsenal of developers and testers for limiting the cost associated with finding and fixing bugs.
Before moving further ahead, it is necessary to comment on the continued analytical work performed during test design. As previously noted, tentative approaches are mapped out in the test analysis phase. During the test design phase of test development, those tentatively selected techniques and approaches must be evaluated more fully, until it is “proven” that the test’s objectives are met by the selected technique. If all tentatively selected approaches fail to satisfy the test’s objectives, then the tester must put his test analysis hat back on and start looking for more alternatives.