Testing the Requirements
It’s hard to visualize how a system will function just by reading the requirements specification. Designing tests based on requirements will help make the expected system behaviors more tangible to all the project participants. And the simple act of designing tests often reveals many problems with the requirements long before you execute the tests on an operational system. In fact, if you begin developing tests as soon as portions of the requirements stabilize, you’ll usually discover correctable-problems quickly and inexpensively.