Benefits of White Box Testing

There are many benefits to white box testing, including the following:

• Analyzing source code and developing tests based on the implementation details enables testers to find programming errors quickly. For example, a white box tester looking at the implementation can quickly uncover a way, say, through an error handling mechanism, to expose secret data processed by a component. Finding such vulnerabilities through black box testing require comparatively more effort than found through white box testing. This increases the productivity of testing effort.
• Executing some (hard to set up) black box tests as white box tests reduces complexity in test setup and execution. For example, to drive a specific input into a component, buried inside the software, may require elaborate setup for black box testing but may be done more directly through white box testing by isolating the component and testing it on its own. This reduces the overall cost (in terms of time and effort) required to perform such tests.
• Validating design decisions and assumptions quickly through white box testing increases effectiveness. The design specification may outline a secure design, but the implementation may not exactly capture the design intent. For example, a design might outline the use of protected channels for data transfer between two components, but the implementation may be using an unprotected method for temporary storage before the data transfer. This increases the productivity of testing effort.
• Finding”unintended” features can be quicker during white box testing. Security testing is not just about finding vulnerabilities in the intended functionality of the software but also about examining unintended functionality introduced during implementation. Having access to the source code improves understanding and uncovering the additional unintended behavior of the software. For example, a component may have additional functions exposed to support interactions with some other component, but the same functions may be used to expose protected data from a third component. Depending on the nature of the”unintended” functionality, it may require a lot more effort to uncover such problems through black box testing alone.