In the case mentioned, that is just the specification that we use to say that a circuit must accept electronic interference and that it does not fail. Usually FCC specifications (in the USA) say that you must accept interference even if it causes undesirable behaviors in your hardware.
In order to tell if something "failed", we usually have a checksum scheme. In hardware, we are good a passing the logic and the complimented logic. I generally put these into an XOR gate and if all of the bits are a "1" in the XOR result tree, I know that things went well. This will let you know if you need to re-run something. I'm sure that in the case in the book, it has nothing to do with attacking the cipher.
To look at the EMI outputs, we just use a network analyzer that can operate at the frequency range of the clock in the system. If you want to attack the cipher, you use the same type of equipment; however, it's a lot easier with clock control. With clock control and access to a power bus, you can extract a lot of information.