Several Profitability and Cost Management features help you validate an application.
Tracing allocations, Performing an Allocation Trace, can help you see the "big picture" of allocation flows.
Rule balancing enables you to view dimension/member combinations within an application to confirm that allocations are working the way you expect (Rule Balancing for Application Validation).
Validation and system reports enable you to identify and diagnose logic and system issues (Performing Validation Analysis for Profitability and Cost Management).
Model views assist with rule balancing and queries (Creating and Managing Model Views).