Scala plugin lets you use ScalaTest testing tool, available for download at ScalaTest for Scala 2.7
When you add a ScalaTest library to your project, write an implementation of org.scalatest.Suite class, and then you will be able to run by just pressing Ctrl+Shift+F10:
After running this class you'll get following tree (actual view depends on your real test results, of course):
If you have more than one test in a package, you can run them all by right-clicking package and selecting Run Tests in menu item.
Things like VM options can be configured in the Run Configuration settings: