Allows summoning objects from DI in tests via ZIO environment intersection types

trait PetStore[F[_, _]] {
  def purchasePet(name: String, cost: Int): F[Throwable, Boolean]
}

trait Pets[F[_, _]]
  def myPets: F[Throwable, List[String]]
}

type PetStoreEnv = Has[PetStore[IO]]
type PetsEnv = Has[Pets[IO]]

val store = new PetStore[ZIO[PetStoreEnv, _, _]] {
  def purchasePet(name: String, cost: Int): RIO[PetStoreEnv, Boolean] = ZIO.accessM(_.get.purchasePet(name, cost))
}
val pets = new Pets[ZIO[PetsEnv, _, _]] {
  def myPets: RIO[PetsEnv, List[String]] = ZIO.accessM(_.get.myPets)
}

"test purchase pets" in {
  for {
    _    <- store.purchasePet("Zab", 213)
    pets <- pets.myPets
    _    <- assertIO(pets.contains("Zab"))
  } yield ()
  // : ZIO[PetStoreEnv with PetsEnv, Throwable, Unit]
}

Lambda parameters and environment may both be used at the same time to define dependencies:

"test purchase pets" in {
  (store: PetStore[IO]) =>
    for {
      _    <- store.purchasePet("Zab", 213)
      pets <- pets.myPets
      _    <- assertIO(pets.contains("Zab"))
    } yield ()
    // : ZIO[PetsEnv, Throwable, Unit]
}