decorator2.md

val input: Seq[RawListing] = //... fixture
def transform(in: RawListing): FullListing = //... trivial
var savedResult: String = null
def save(json: String): Async[Unit] = Async {
  insertResultHere = json
}
val expectedResult = //... actually generate some sort of JSON

val processor = new ListingProcessor(transform, save)
processor.processListings(input)
//... resolve asynchrony

assertEquals(expectedResult, savedResult) // Or regex acrobatics, etc