Add defaultIfEmpty tests
Add defaultIfEmpty tests

cfraz89/RxSwift,kzaher/RxSwift,cfraz89/RxSwift,cfraz89/RxSwift,ReactiveX/RxSwift,kzaher/RxSwift,cfraz89/RxSwift,ReactiveX/RxSwift,ReactiveX/RxSwift,kzaher/RxSwift,kzaher/RxSwift