How to test actors?

I have an actor , which on one of the messages run this method :

def addAuctions(actions:List[String]): Unit = {
var i = 0
for(auction <- actions) {
  val x = context.actorOf(Props(new Auction(auction, AUCTION_LIMIT_IN_SECONDS, self)), "auction" + i)
  x ! Auction.Init
  i= i+1
}

}

Then I have a following test :

"seller" in {
  val seller = system.actorOf(Props[Seller],"seller")
  seller ! Seller.NewAuctions(List("Laptop"))

  // HERE - HOW TO TEST IT ?

}

How Can I test if seller send message Auction.Init ?