query SelectionOfUnion {
  pet1
  pet2
  pet3
  pet4
  pet5
  pet6
}

type Query {
  pet1: CatOrDog,
  pet2: CatOrDog!,
  pet3: [CatOrDog],
  pet4: [CatOrDog!],
  pet5: [CatOrDog]!,
  pet6: [CatOrDog!]!,
}

type Cat { id: String! }
type Dog { id: String! }
union CatOrDog = Cat | Dog