Narrowband IoT (NB-IoT) stands for a radio access technology standardized by the 3GPP organization to enable a large set of use-cases for massive machine-type communications (mMTCs). Compared to legacy human-oriented 4G communication systems, NB-IoT has game-changing features in terms of extended coverage, enhanced power saving modes, and a reduced set of available functionalities. At the end of the day, these features allow for connectivity of devices in challenging positions, enabling long battery life and reducing device complexity. This article addresses the development of the universal testing device allowing for in-depth verification of NB-IoT communication parameters. The presented outputs build upon cooperation between the Brno University of Technology and Vodafone Czech Republic a.s.