Scala dependency injection with traits

package.scala

package com.joescii

package object code {
  val DbThing = new DbThingImpl()
  val HttpThing = new HttpThingImpl()
  val BizThing = new BizThingImpl(DbThing, HttpThing)
  
  trait DbThing {
    def getDbStuff(params):Future[DbStuff]
  }
  
  trait HttpThing {
    def getHttpStuff(params):Future[HttpStuff]
  }
  
  trait BizThing {
    def doComplicatedStuff(params):Future[BizStuff]
  }
  
  private [code] class DbThingImpl extends DbThing {
    override def getDbStuff(params):Future[DbStuff] = ???
  }
  
  private [code] class HttpThingImpl extends HttpThing {
    override def getHttpStuff(params):Future[HttpStuff] = ???
  }
  
  private [code] class BizThingImpl(db:DbThing, http:HttpThing) extends BizThing {
    override def doComplicatedStuff(params):Future[BizStuff] =
      db.getDbStuff(params).zip(http.getHttpStuff(params)).map { 
        case (dbStuff, httpStuff) => ???
      }
  }
}

I was going for something like what @sleepynate did. Just separate out the purecode (f) from the impure side-effecting code (BizThingImpl). That way you can unit test f easily and then integration test BizThingImpl with Wiremock etc.

@pellunutty's solution looks pretty nice. Because M is a Monad you could substitute Future with the Identity Monad for your tests (or any other Monad you want to).