Neutrality
Fall of Rome is a dynamic game, where allies easily become enemies, and enemies often become allies. The Team Game playtest has revealed that it must be possible to change a declaration after it has been made. This includes issueing a declaration of neutrality with another player, representing a halt to hostilities, or compatriots that have drifted apart.
Fortunately, the programming logic for declarations was well encapsulated. Changing the declaration type representation from a java boolean (ally / enemy) to a tri-state (adding neutrality) was quick and painless, thanks due to the suite of junit tests that verified everything still worked after the refactoring.