A method, device and computer program for generating wireless signals for testing a network node for transmitting Narrow Band Internet of Things signals, for compliance with predetermined criteria, the network node being configured to support multiple carriers and to support operation within at least one radio frequency bandwidth. The method comprises: controlling a wireless signal generator to generate one test signal in a frequency band towards one edge of one of the at least one radio frequency bandwidth and one further test signal in a frequency band towards the other edge of the same one of the at least one radio frequency bandwidth, the one test signal comprising a Narrowband Internet of Things test signal.