Using white box approach to test design

Using white box approach to test design

In the previous chapter the reader was introduced to a test design approach that considers the software to be tested as a black box with a well-defined set of inputs and outputs that are described in a specification. In this chapter a complementary approach to test case design will be examined where the tester has knowledge of the internal logic structure of the software under test. The tester‘s goal is to determine if all the logical and data elements in the software unit are functioning properly. This is called the white box, or glass box, approach to test case design. The knowledge needed for the white box test design approach often becomes available to the tester in the later phases of the software life cycle, specifically during the detailed design phase of development. This is in contrast to the earlier availability of the knowledge necessary for black box test design. As a consequence, white box test design follows black box design as the test efforts for a given project progress in time. Another point of contrast between the two approaches is that the black box test design strategy can be used for both small and large software components, whereas white box-based test design is most useful when testing small components. This is because the level of detail required for test design is very high, and the granularity of the items testers must consider when developing the test data is very small. These points will become more apparent as the discussion of the white box approach to test design continues.