Black box testing and white box testing offer two different means of testing software. While one is not inherently “better” than the other, both forms have specific advantages and disadvantages that must be weighed against the needs of the tester. These two forms are not mutually exclusive, and “gray box testing” adopts features of both.
Black box quality testing checks software solely for results in a way that does not require programming knowledge or understanding of software code. In this form of result-based testing, the tester simply knows that a certain input should produce a corresponding output; the tester has no knowledge of how the software actually creates the output. Some typical test methods include state transition tables, limit value analysis, and error assumption.
The strengths and weaknesses of black box testing depend on the simplicity of outcome-based testing and the lack of technical knowledge required. In short, it’s simpler to implement, but that simplicity limits the scope of testing. Most programs have thousands, if not millions, of inputs, making it virtually impossible to test every input/output. Because no specialized knowledge is required, it is easier and cheaper to create test kits. Even so, regular software changes tend to break these tests due to its reliance on a stable interface, which could lengthen testing and increase costs. Finally, black box quality testing has the potential for greater objectivity because all testing is done from the user’s point of view; the designer is usually not part of the process.
A software white box test verifies the inner workings of whatever is being tested. It requires in-depth knowledge of software code, as well as the programming skills necessary to fix bugs. Some examples of white box testing include mutation testing, code coverage, and fault injection.
White box quality testing is much more efficient than black box testing when debugging programming code. White box testers will find bugs more quickly due to their working knowledge of the software, but this experience and training add to the cost. This cost can be covered by automated testing of isolated areas of the programming code. White box testing also has a hard time testing for unpredictable common user behavior. You can only test advance tickets; these typically do not include the experimental or ill-conceived ideas of the average person.
With large teams, extensive testing of any software often incorporates both types; this is called a layered or gray box test. Gray-box quality testing often involves a black-box group submitting bug reports to a white-box team, or a white-box group validating bug fixes through input from the other testers.
The question of whether to use black box, white box, or gray box testing can only be answered when developers consider their needs, budget, and the complexity of their software. Even so, almost all contemporary software development uses gray box quality testing as a natural part of the alpha and beta release process.
