I am having few validation rules on Opportunity, which should be fired when
"Closed Won". An example validation rule is shown below
AND ( ISPICKVAL(StageName, 'Closed Won'), ISBLANK( SomeOppField__c ) )
Opportunity > StageName = "Closed Won" happens after Approval > Field Update.
Somehow none of the validation rule fires after Opportunity is approved to closed won, my requirement is to block approval process, if data on opportunity is missing.