Testing EMC requires access to an electrically isolated chamber called an anechoic chamber. From here a special array of antennae can be used to measure the devices radiated emissions, spectrum analyzers are used for conducted.
In the anechoic chamber, they will test radiated emissions (interference that travels through the air) and conducted emissions (interference that travels through cables) with an antenna.
For radiated emissions tests they will test the DUT at different heights and directions to find the point in the air where the in-air interference is the worst.