Answer
Role swaps should be tested often enough that the procedure stays routine, the application dependencies stay current, and leadership can trust the continuity promise being funded. The exact cadence depends on workload criticality and change rate, but the important point is that testing must be scheduled, evidenced, and reviewed instead of deferred indefinitely.
Buyers should ask whether the software makes rehearsals practical without creating excessive production risk. If every test feels too disruptive to run, confidence in the HA design will decay quickly.