Although test has always been thought of as a necessary evil, in reality it is the single best way to ensure that a product meets the needs of your customer. Throughout the development process test is used to reduce the risk that the design, theory, and final product, reality, are as close to each other as possible. The SMTA/TMAG Testability Guidelines TP-101E was developed by various Task Forces, each concentrating on its own discipline. The work of the various Task Forces is featured as separate chapters. The Guidelines were intended to assist the reader in dealing with the testability considerations that need to go into the design, development, and test of a product.