In the present method for use in verification of a device, a plurality of injection flags are provided, each of which is associated with one of a plurality of packet classes. Each injection flag may be of a first or a second state. Next, a packet is generated. If the injection flag of the packet class of the generated packet is in the second state, it is indicated that a packet of that packet class has already been generated, and the device is not tested. If the injection flag of the packet class of the generated packet is in the first state, the device is tested and the injection flag of the packet class of the generated packet is set to the second state. The process is repeated, the running of subsequent tests being determined by the state of the injection flag of the packet class of the generated packet.