How to test that an actor created at the start of a Play! application receives a message?

For every client connecting to my Play! 2.5 Scala application, a webSocket is opened.

I have an actor created at the beginning of the application with AkkaGuiceSupport :

bindActor[RoomsActor]("rooms")

When a webSocket is opened, it sends a message to this actor and I want to test that the message is well sent.

How can I do this?