throwingStub.swift

func stub<I,O>(of: (I) throws -> (O)) -> (I) throws -> (O){
  return nil!
}
func niceStub<I,O>(of: (I) throws -> (O), thatReturns: O) -> (I) throws -> (O){
  return { _ in thatReturns }
}
func niceStub<I,O,E:Error>(of: (I) throws -> (O), thatThrows error: E) -> (I) throws -> (O){
  return { _ in throw error }
}
func niceStub<I,O: DefaultProvidable>(of: (I) throws -> (O)) -> (I) throws -> (O){
  return { _ in O.defaultValue }
}
func spyCalls<I,O>(of stub: inout (I) throws -> (O)) -> (ArgRecords<I>) {
 .... // copy&paste implementation of spyCalls
}