Easy Trait Testing in Scala

Scala has the notion of a trait, which is also sometimes referred to as a mixin. Traits are similar to interfaces in the Java world, but allow for partial implementations. This provides a convenient (and predictable) way of adding concrete implementations from a number of Traits to a single class. Say you have a simple trait such as:

trait Storage {
  val storageName: String
  require(storageName != null && storageName.nonEmpty)
  def getStorageName = storageName
}

You’re writing a bunch of tests and would prefer not to instantiate an actual Storage class, instead you would rather test the trait itself. You can just do something like:

new {
  val storageName = "Testing"
} with Storage {
  assert(getStorageName != null)
  assert(getStorageName nonEmpty)
  assert(getStorageName equals "Testing")
}

The above code creates an anonymous class that fulfills the abstract requirements of Storage, and calls a few assertions to verify the implementation. There are some potential downsides to doing this type of instantiation but for quick tests it’s quite handy.