Then, a function that uses the incremented appealCount is called to check what the cost is supposed to be.
E.g. Create Dispute: 1e15 ETH
Call Appeal Cost: 1e15 ETH
call appeal{value: 1e15} -> the appealCount gets incremented, appealCost(_disputeID, _extraData) is now 2e15, so reverts with:

[FAIL: InsufficientPayment(1000000000000000 [1e15], 2000000000000000 [2e15])] 

found on a test here: greenlucid/pgtcr#1