The article deals with the testing problem that arises when developing devices for the Internet of Things (IoT) systems. Smart devices that provide data transmission over the Internet are becoming more and more popular. For example, energy metering devices that transmit data wirelessly are an integral part of the Internet of Things system in the housing and utilities sector. Currently, the firmware testing of water and heat consumption meters is performed manually. The manufacturer must spend a significant number of man-hours on this work. The article describes the results of research work on the development of an automated testing system. The experimental basis of the study is a static three-phase universal multi-tariff electric energy metering device Milur 307 with the Karat-941LW module. The meter has a built-in specialized microcontroller of the Russian manufacturer "Milander". The device is equipped with communication interfaces for data exchange with external devices. The subject of testing is the embedded software of the Karat 941LW interface module, which implements the top-level application data exchange protocol. For testing IoT devices, the authors have developed a special service-the testing core. The service polls the device according to the specified scenario recorded in the YAML file. The survey is conducted via the MQTT protocol, which is used by the LoRaWAN network server. As a result of testing, a report is generated. The developed testing methodology will be used to create a universal testing platform for devices operating over a wireless data network.