Boundary Value Analysis is a black-box testing technique that is used to test the boundaries or limits of input or output values for a given system or component. Boundary Value Analysis helps to identify errors at the edges of an input or output domain. For example, in a system designed to work out the employee tax to be paid, there are four boundaries for the salary input: $4,000 (lower boundary for tax free), $5,500 (upper boundary for tax free and lower boundary for 10% tax), $34,000 (upper boundary for 10% tax and lower boundary for 22% tax), and any value above $34,000 (upper boundary for 22% tax and lower boundary for 40% tax). A valid Boundary Value Analysis test case would test one value below, on, and above each boundary. For example, $33,501 is a valid test case because it is one value above the boundary of $34,000. A detailed explanation of Boundary Value Analysis can be found in [A Study Guide to the ISTQB® Foundation Level 2018 Syllabus], pages 38-41.