Using a class

Let's have a look at how DoubledMultiplierIdentity, which we saw previously, would be tested. One would try to simply mix the trait into a test class and test the methods:

class DoubledMultiplierIdentityTest extends FlatSpec with ShouldMatchers with DoubledMultiplierIdentity

This, however, won't compile and will lead to the following error:

Error:(5, 79) illegal inheritance; superclass FlatSpec
 is not a subclass of the superclass MultiplierIdentity
 of the mixin trait DoubledMultiplierIdentity
class DoubledMultiplierIdentityTest extends FlatSpec with ShouldMatchers with DoubledMultiplierIdentity {
^

We already talked about this before and the fact that a trait can only be mixed in a class that has the same super class as itself. This means that in order to test the trait, we should create a dummy class inside our test class and then use it:

package com.ivan.nikolov.linearization

import org.scalatest.{ShouldMatchers, FlatSpec}

class DoubledMultiplierIdentityTest extends FlatSpec with ShouldMatchers {

  class DoubledMultiplierIdentityClass extends DoubledMultiplierIdentity

  val instance = new DoubledMultiplierIdentityClass

  "identity" should "return 2 * 1" in {
    instance.identity should equal(2)
  }
}