How to test stackable trait

Question

Suppose I have such trait:

trait FooStackable {

  def foo: String

  def bar: Double



  abstract override def logic(x: Double): Unit = {

    if (x < 0) println(foo)

    else super.logic(bar + x)

  }

}

I want to write a test on the method

logic

for this trait in behaviour driven style: I want to check in test depending on input parameters what method was called and how many times. Apparently it's not possible simply to instantiate an instance of this trait(even when overriding unimplemeted methods), so mocks also will not work.

Does it make sense to write such test scenarios? (Real logic in method

logic

is more complex) And if yes how stackable traits are tested in isolation?

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Answer 1

The code cannot be compiled as written. In particular, there is no 'super' in this trait as it is not derived from anything. I made some changes to work around it:

trait Stackable {
  def logic(x: Double): Unit
}

trait FooStackable extends Stackable {
  def foo: String
  def bar: Double

  abstract override def logic(x: Double): Unit = {
    println("In FooStackable.logic()")

   if (x < 0) println(foo)
    else super.logic(bar + x)
  }
}

trait TestStackable extends Stackable {
  def logic(x: Double): Unit = {
   println("In TestStackable.logic()")
  }
}

object FooStackableTest extends TestStackable with FooStackable {
  def foo: String = "foo"
  def bar: Double = 1.234

  override def logic(x: Double): Unit = {
   println("In FooStackableTest.logic()")

   super.logic(x)   
  }
}

With these changes FooStackable now sits in the middle between TestStackable (which implements logic() in a base class) and FooStackableTest (implements other undefined members of FooStackable and overrides logic()):

scala> FooStackableTest.logic(4.0)
In FooStackableTest.logic()
In FooStackable.logic()
In TestStackable.logic()

scala> FooStackableTest.logic(-4.0)
In FooStackableTest.logic()
In FooStackable.logic()
foo

scala>

How to test stackable trait

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