Echoing the advice here, I wouldn't call injecting the database in the constructor dirty. It might have plenty of benefits, including decoupling actor behaviour from the particular database instance.
However if you know there is only ONE database you will be always using in your production code, then think about defining a package level accessible constructor and a companion object returning a Props object without parameters by default.
Example below:
object MyActor {
def props() : Props = Props(new MyActor(new Database()))
}
class MyActor private[package](database : IDatabase) extends Actor {
def receive = { ... }
}
In this case you will still be able to inject the test database in your tests case (given the same package structure), but prevent users of your code from instantiating MyActor
with unexpected database instance.