What kind of testing allows testers to use knowledge about code and design?

White box testing is the correct choice as it involves the tester having an understanding of the internal workings of the application, including its code and design. This type of testing allows for a thorough examination of the logic, structure, and flow of the software. Testers can create test cases based on the knowledge of the code structure, algorithms, and other specific design elements, ensuring that all paths and conditions in the code are executed and verified.

By accessing this level of detail, testers can identify potential vulnerabilities, logical errors, and omissions in the code that may not be apparent through other forms of testing, such as black box testing, where the tester has no knowledge of the internal workings and focuses solely on the output generated from given inputs. This foundational understanding allows for deeper and more effective testing strategies, making white box testing essential for ensuring quality in software development.