To validate role-based security in a Power BI dataset, what action should be taken?

To validate role-based security in a Power BI dataset, activating the "View As" feature in Report view is the most effective approach. This feature allows you to simulate the role-level permissions applied to different users or user groups directly within the report. By doing so, you can ensure that the security roles defined for the dataset function as intended, granting or restricting access to specific data as per the defined criteria.

Using "View As," you can select different roles that have been created in the dataset and see the report from the perspective of a specific user or group. This way, you can dynamically verify what data a specific role can or cannot access, confirming that security roles are set up correctly before deploying the report to end users.

The other options, while they may have valid use cases in different contexts, do not specifically validate role-based security. For example, adding a conditional column is useful for data manipulation and transformation but does not directly address role security. Implementing a DAX expression filter is also geared towards data visibility and could be a part of role-based security, but it's not a validation step. Creating a what-if parameter involves scenarios and modeling but does not pertain to validating access permissions reflected by role-based security.