Overriding a method which returns Unit while writing unit test cases

I am writing unit test cases using MockitoSugar.

Here is my sample code:

class EmployeeRepo{

    def addEmplyees(emp:Employee):Long={
    //logic
    val res1 = sendReport
    val res2 = sendNotification
    //logic
    }

    def sendReport:Boolean={
    //logic
    }

    def sendNotification:Unit={
    //logic
    }
}

Sample test case:

class TestEmployeeRepo extends WordSpec with MockitoSugar with ScalaFutures{

    "TestEmployeeRepo" must {
    "add employee" in {
    //mock statements
    val result = MockEmployeeRepo.addEmplyees(emp)
    //assert statements
    }

  }

}


object MockEmployeeRepo extends EmployeeRepo{

    override def sendReport:Boolean = true

    override def sendNotification:Unit = //needs unit
 }

Here in the above piece of code I am trying to test addEmployee method with necessary mocking. So while overriding sendNotificationwhich actually returns Unit, I am not sure how should I return Unit.

I tried these two ways:

override def sendNotification:Unit = println("")

override def sendNotification:Unit = Unit

Working fine, but please suggest me the right way to follow and what should be there at //needs unit. Thanks in advance.