Demonstrates using multiple traits to mix in multiple "Before" hooks, with an intended usage in creating re-usable and composable execution contexts for test cases.

Test_hook_trait_composition.scala

//
// A demonstration of using multiple traits to mix in multiple "Before" hooks,
// with an intended usage in test code.
//
// The demonstration shows that multiple traits inheriting BeforeEach (or more
// germanely scalatest's BeforeAndAfterEach) can be sufficiently composable to use
// in our testing toolchain without sewing our own strait jacket.
//

object Main {
  def main(args: Array[String]) {
    println("Both of these should print the same thing.")
    println("Output from test class that clears persistence separately:")
    new MyTestsThatAnnihilatePersistencesOneMixinAtATime().beforeEach
    
    println("")
        
    println("Output from test class that clears persistence in one mixin:")
    new MyTestsThatAnnihiliateAllPersistencesWithOneMixin().beforeEach
   
    /* Both lines print:
     *   Clearing Validation
     *   Clearing Cache
     *   Clearing Database
     */
  }
}

class MyTestsThatAnnihilatePersistencesOneMixinAtATime
  extends ClearDatabaseBefore
  with ClearCacheBefore 
  with ClearValidationBefore


class MyTestsThatAnnihiliateAllPersistencesWithOneMixin extends ClearAllPersistence


trait ClearAllPersistence 
  extends ClearDatabaseBefore
  with ClearCacheBefore
  with ClearValidationBefore


trait ClearDatabaseBefore extends BeforeEach {
  override def beforeEach {    
    println("Clearing Database")
    super.beforeEach()
  }
}


trait ClearCacheBefore extends BeforeEach {
  override def beforeEach {
    println("Clearing Cache")
    super.beforeEach()
  }
}


trait ClearValidationBefore extends BeforeEach {
  override def beforeEach {
    println("Clearing Validation")
    super.beforeEach()
  }
}


trait BeforeEach {
  def beforeEach() { }
}