Testing modbus integration

I’m trying to improve the climate entity in Modbus integration. The improvement includes adding more registers that reflect and control the device mode. The code is working fine against the hardware, but I want to add some test in order to have it merged into HA. Walking through the Modbus test, it seem as if the test can only inject a single value to a holding register. Is there a way to mock multiple values in multiple addresses using the existing code?

This project (https://github.com/gazoodle/CenturyVSPump / Pool pump speed control - easy way? - #2 by gazoodle) has some customization to send and custom Modbus data that doesn’t adhere to the typical sort of commands and responses.

My problem is how to test the changes I made using HA testing framework.