Testing is intended to show that a program does what it is intended to do. Why may testers not always know what a program is intended to do?
Choosing not inform the software tester about the use cases of your software might prove to be a beneficial testing strategy. It allows the tester to approach the testing with an open mind, and interact with the software in the same manner your intended end-users will.
Software Testing requires a fresh perspective.
A neutral person who behaves as close to the end-user as possible is needed to perform a thorough Behavioral, Specification-Based, Input-Output Testing