SOM is an entire CPU architecture built in a small package, of size like a credit card. It is a board-level circuit that integrates a system function and provides core components of an embedded processing system - processor cores, communication interfaces, and memory blocks on a single module. Designing any product based on the SOM is a much faster process than designing the entire system from the ground up.
There are multiple System on Module manufacturers available in the market worldwide with an equal amount of open-source automated testing frameworks. If you plan to use System-on-Module (SOM) in your product, the first thing required is to identify the test automation framework from the ones available out in the market and check for a suitable module for your requirement.