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In the field of software testing, there are various methods used all with the end goal of creating error- and bug-free code. You’ve probably heard of white-box testing and black-box testing—so what are these types of testing used for, and how are they different?

The difference between these two types of testing boils down to one thing: whether or not the software tester knows the inner workings of the software they’re testing. This key difference is important because it can have a direct effect on the results of the test.

White-box Testing

If a tester is intimately familiar with the implementation, design, and structural aspects of the software they’re testing, they can “see inside the box” and see how the software is put together, hence the name white-box, or “clear box.” Because they engineered or understand the desired inputs and outputs, they can test the outcomes against their expectations.

White-box testing also differs in that it focuses on the inner workings and structure of software, not its functionality for the user. It’s more like looking under the hood of a car and testing the engine’s workings. While it most commonly happens during the unit testing phase, white-box testing can occur during regression testing, integration testing, or systems testing.

White-box testing is generally considered to be low-level testing and can be performed on software before the user interface (UI) is developed, making it a wise measure to take in earlier phases of a software’s development. It makes it possible to test a software’s inner workings thoroughly before the UI has been created, which ensures testing is happening more often, and more early on—all good things for having the most sound code possible when it comes time to launch.

Note that, with all unit testing, writing the testing scripts can be time consuming and the scripts need to be maintained and updated as the software’s implementations change. Testing is a commitment, but a very valuable one.

Black-box Testing

If a tester is not familiar with the implementation, design, and structural aspects of the software they’re testing, they cannot “see inside the box” to know exactly how the software executes input into output, hence the name black-box. This makes black-box testing more functional testing, by design—a tester is not looking at the structural elements, but rather if the software performs how it’s supposed to. The results of black-box testing can uncover behavioral or performance errors in the interface, issues with data retrieval, problems with launch or crashing, and functions that don’t perform properly vs. expectations. In this respect, it’s a more broad testing than white-box, and requires a tester to interact with the software in order to verify if inputs and outputs are working properly—without knowing exactly how it’s being executed inside “the black box.”

Black box testing is more high-level testing vs. white-box, and is often used in penetration testing, an arm of security engineering that involves attempting to (safely) hack into software to find potential vulnerabilities with the end goal of patching them up, but can also be implemented during integration testing and system testing.

There are a few advantages to black-box testing, one of which is the fresh perspective a tester who isn’t intimately familiar with a project can provide. Also, your black-box tester doesn’t have to have a lot of programming experience—the test cases they’re focusing on are more user-based. With white-box testing, the testers are always software developers.

Learn more about the different types of testing, or read up on the difference between manual testing and automated testing.