Typical ICT uses a 'bed of nails' to make connection. This is an array of spring probes that contact the PCB, usually by pulling the board down on to them with a vaccuum pump although 'flying probe' systems are available. Behind the probes is a multiplexer which routes voltages and test instruments to the desired combination of probes to make two or four wire measurements and sometimes to apply 'guard' potentials to isolate unwanted current paths.
The ICT 'fixture' (the bed of nails) has to be designed so the probes are located where the connections points to the circuit are located on the PCB. For through-hole components the coordinates can be extracted from the PCB drill file but probing the pins of surface mounted devices is a bad idea because the probe pressure could push the pin against the track below it and hide a dry-joint fault. For SMD, small pads joined to the test nodes is a better method but this has to be incorporated at the PCB design stage.
You really have to design with ICT in mind from the start, if you don't, the testability will be limited or impossible.
Brian.
(trained in Fairchild, Genrad and HP ICT systems!)