'Design for Test' is a broad term that has nothing to do with IC's or any specific circuit.
Another term is 'Design for Manufacture'
It is describing a principle whereby, when designing a printed circuit board or electronic module, consideration should be taken into account to make the manufacture and the testing of the product as simple as possible.
Some complex ic's have 'Boundary Scan' and 'JTAG' interface. This is onboard circuitry in the IC that allows testing of the IC function and I/O pins.