1. Compare all the artifacts between existing and upgraded environment to make sure that if any any new properties / fields added to existing. ( we use beyond compare to compare the complete XML code)
2. re-execute the consolidation from the inception and make sure that there is no change in the data before and after.
3. Compile all the business rules and look for any errors, warning in existing environment and make sure that they are same after upgrade.
4. Make sure that all the application functionalities are working same as existing environment ( Reports, WF's CV,s business rules, consolidation, calculation, task manager, batch jobs, data management jobs, openng/closing periods etc...).
5. Let the business test each of the function.