Design for testability (DFT) works to make a circuit more testable to ensure that it was manufactured correctly. Alfred Crouch explains the purpose of DFT in his book, Design-For-Test for Digital ICs ...
JTAG has its place but it is not by any means the total solution. Boundary scan, as standardized by IEEE 1149.1 and commonly referred to as JTAG, has truly revolutionized the testability of circuit ...