An integral part of the overall design effort of electronic systems is testability engineering. The reason for this importance is that testability engineering addresses the requirements for testing that must be considered in the development and design of an electronic system or systems. This includes the extent to which a system or system design supports fault detection and fault isolation in a confident, timely, and cost-effective manner. Historically, testability began as a subset of the maintainability engineering process. However, in recent years, electronic designs have become so complex, especially with multiple layers of redundancy, that testability has been established as a separate and distinct engineering activity. Testability engineering is intimately involved with both reliability and maintainability.

As stated previously, reliability engineering focuses on making the design as failure-free as possible, and maintainability focuses on making the design as easy and cost-effective to repair as possible when it does fail. Testability is actually a bridge between reliability and maintainability. Before the failure can be fixed, it must be identified. And before testing can be planned, the possible failures that may occur in a system must be predicted. Therefore, testability is the link between reliability, where possible failures are identified, and maintainability, where the failures are fixed. The degree of testability exhibited by a system design is in direct correlation with achievement of maintainability goals. This is accomplished through incorporation of adequate testability, including built-in test, into the design. The easier and quicker faults are located and identified, the more...