Illustrates why inheritance produces unexpected behavior when an entity may also service as a reference.

EntityReferenceSpec.scala

import org.scalamock.scalatest._
import org.scalatest._

import scala.language.implicitConversions

class EntityReferenceSpec extends WordSpec with MockFactory {

  "An entity" that {
    "is also a reference" when {

      "subclassing" must {
        trait MyRef { def id: Long }
        case class MyEntity(id: Long, name: String) extends MyRef
        case class MyRefImpl(id: Long) extends MyRef

        trait MyService {
          def get(ref: MyRef): MyEntity
        }

        "satisfy expectation" in {
          val service = mock[MyService]
          (service.get _).expects(MyRefImpl(100)).returns(MyEntity(100, ""))
          service.get(MyEntity(100, ""))
        }
      }

      "implicitly converted" must {
        case class MyEntity(id: Long, name: String)
        case class MyRef(id: Long)
        object MyRef {
          implicit def implyMyRef(entity: MyEntity): MyRef = MyRef(entity.id)
        }

        trait MyService {
          def get(ref: MyRef): MyEntity
        }

        "satisfy expectation" in {
          val service = mock[MyService]
          (service.get _).expects(MyRef(100)).returns(MyEntity(100, ""))
          service.get(MyEntity(100, ""))
        }
      }

    }
  }

}

output

sbt:entity-reference> testOnly EntityReferenceSpec
[info] EntityReferenceSpec:
[info] An entity that
[info]   is also a reference
[info]     when subclassing
[info]     - must satisfy expectation *** FAILED ***
[info]       Unexpected call: <mock-1> MyService.get(MyEntity(100,))
[info]       
[info]       Expected:
[info]       inAnyOrder {
[info]         <mock-1> MyService.get(MyRefImpl(100)) once (never called - UNSATISFIED)
[info]       }
[info]       
[info]       Actual:
[info]         <mock-1> MyService.get(MyEntity(100,)) (Option.scala:121)
[info]     when implicitly converted
[info]     - must satisfy expectation
[info] ScalaTest
[info] Run completed in 143 milliseconds.
[info] Total number of tests run: 2
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 1, failed 1, canceled 0, ignored 0, pending 0
[info] *** 1 TEST FAILED ***
[error] Failed: Total 2, Failed 1, Errors 0, Passed 1
[error] Failed tests:
[error]         EntityReferenceSpec
[error] (Test / testOnly) sbt.TestsFailedException: Tests unsuccessful
[error] Total time: 0 s, completed Aug 3, 2018, 10:43:52 AM