You will need high input power supply, high voltage/high power probes to test it. You may implement some voltage/current diver circuit to scale down the system. Reading related articles and how they build experimental setup for that will be helpful. Articles regarding high power high voltage DC-DC converter may give you important information. One such article is:

1.G. Ortiz, M. G. Leibl, J. E. Huber and J. W. Kolar, "Design and Experimental Testing of a Resonant DC–DC Converter for Solid-State Transformers," in IEEE Transactions on Power Electronics, vol. 32, no. 10, pp. 7534-7542, Oct. 2017, doi: 10.1109/TPEL.2016.2637827.

For isolated converter you can also separately make a partial discharge test of your transformer. The below paper talks about high power transfer experiment. This paper and its references may also be helpful

Rahman, S., Candan, M.Y., Tamyurek, B. et al. Design and implementation of a 10 kV/10 kW high-frequency center-tapped transformer. Electr Eng 104, 2603–2619 (2022). https://doi.org/10.1007/s00202-022-01499-3

Hope this will help you.

Thank u so much