When testing beacons and Bluetooth LE, nRF Connect is usually sufficient. However, if you need deeper analysis of Bluetooth you need to use a packet sniffer.
NCC Group has a new open source sniffer for Bluetooth 5 that also works with Bluetooth 4.x. You need to run the software on a Texas Instruments (TI) CC26x2 board.
The source code and instructions are available on GitHub.