Validation will involve testing the rules and get Subject Matter Expert feedbacks to improve the quality of the rules. A set of tools are available in high end BRMS platform to do some rule conflict analysis, testing, and executing complex queries to understand how rules are impacting others rules result.
The tasks are following a TDD approach, where data scenarios are defined as early as the rule discovery, and tests are developed to integrate the data definition to trigger rule execution in the context of the rule set deployed.