Refactored a `ConstantProperty` test case.
Refactored a `ConstantProperty` test case.

Juraldinio/ReactiveCocoa,sandyway/ReactiveCocoa,walkingsmarts/ReactiveCocoa,victorlin/ReactiveCocoa,RuiAAPeres/ReactiveCocoa,andersio/ReactiveCocoa,ohwutup/ReactiveCocoa,tzongw/ReactiveCocoa,victorlin/ReactiveCocoa,RuiAAPeres/ReactiveCocoa,walkingsmarts/ReactiveCocoa,andersio/ReactiveCocoa,RuiAAPeres/ReactiveCocoa,tonyarnold/ReactiveCocoa,kevin-zqw/ReactiveCocoa,ohwutup/ReactiveCocoa,ohwutup/ReactiveCocoa,smilypeda/ReactiveCocoa,tzongw/ReactiveCocoa,rpowelll/ReactiveCocoa,andersio/ReactiveCocoa,rpowelll/ReactiveCocoa,walkingsmarts/ReactiveCocoa,tzongw/ReactiveCocoa,smilypeda/ReactiveCocoa,kevin-zqw/ReactiveCocoa,calebd/ReactiveCocoa,ReactiveCocoa/ReactiveSwift,tonyarnold/ReactiveCocoa,ikesyo/ReactiveCocoa,rpowelll/ReactiveCocoa,Juraldinio/ReactiveCocoa,calebd/ReactiveCocoa,sandyway/ReactiveCocoa,ReactiveCocoa/ReactiveSwift,Juraldinio/ReactiveCocoa,smilypeda/ReactiveCocoa,victorlin/ReactiveCocoa,ikesyo/ReactiveCocoa,sandyway/ReactiveCocoa,ReactiveCocoa/ReactiveSwift,tonyarnold/ReactiveCocoa,kevin-zqw/ReactiveCocoa,calebd/ReactiveCocoa