Test.scala

val useCase = new BaseUseCase[Int] {
  def execute() = 100
}

var isCalled = false
var useCaseResult: Try[Int] = Failure(new NoSuchElementException)

executor.execute(useCase) { result =>
  isCalled = true
  useCaseResult = result
}

isCalled shouldBe true
useCaseResult shouldBe Success(100)