Network App verification means that the Network App functionality is checked in a synthetic environment in your machine to test that your Network App performs as expected.
In special, it must be tested the communication with the 5G Core APIs (but instead of a real 5GC, using a 5GC NEF emulator), the exposed interfaces (Network App APIs or business APIs) and their compliance with CAPIF (for which is employed the EVOLVED-5G CAPIF testing tool ).
Information regarding how to use the NEF emulator and the CAPIF testing tool, as well as those software artifacts can be found at EVOLVED-5G GitHub.