How do you test 5G Non-Terrestrial Networks Prior to Space Launch?

With the hype growing around 5G non-terrestrial networks providing much larger coverage and resilience compared to terrestrial networks.  If they are to be used for mission critical communications, it is essential that they are reliable, stable and tested cost-effectively before they are launched into space. You must ensure vital requirements are met before deployment. As the NTN standards evolve, with new feature developments and software updates, how can you minimize the risk of failure (when launched) prior to launch?