White-box checks

Just as in black-box testing, in white-box tests, you not only have to decide what test cases to run but also how to check that those tests have passed. When you have access to the code in white-box testing, you can do this at several levels.

At the level of individual lines of code under unit tests, you can specify the exact outputs of the different functions. Once again, this has all the strengths and weaknesses of unit testing – it is precise and comprehensive but cannot find errors when the functions are combined.

While running system tests, white-box knowledge lets testers see the code’s behavior in more detail. This lets you find other classes of issues that might cause subtle or invisible problems for users, such as inefficiencies in the code or two wrongs making a right, as described next.

Checking code inefficiencies

Code inefficiencies can include code that initially tries to do the wrong thing but there are retries, which means...