Test clashes with mixins

MixinClashes.scala

/**
  * Here we create a diamond inheritance structure with trait Client at the
  * bottom. Trait Client inherits the same member from two traits. What does
  * Scalac do here?
  *
  * Answers:
  *
  * - If the two members are abstract and have the same signature, they are
  *   merged and the code is accepted (see helper).
  * - If they have the same signature and both have bodies, the code is
  *   rejected (see helper2).
  * - If they have different signatures which could coexist as overloads, the
  *   code is still not accepted (they don't like Java-like overloading, after
  *   all) (see helper3).
  */

trait Base {
  def sum: Int = ??? //sum "+" sum
}

trait Variables extends Base {
  override def sum = helper
  def helper : Int

  //def helper2 = letter

  //def helper3 : Int => Int
  def letter = ???
}

trait Literals extends Base {
  override def sum = helper
  def helper : Int

  //def helper2 = digit

  //def helper3: String => String
  def digit = ???
}

trait Client extends Literals with Variables