generator and property for ADTs with custom initialization logic

gistfile1.scala

// the ADT
sealed trait Account {
  def no: String
  def name: String
  def openingDate: Date
  def closeDate: Option[Date]
}

final case class CheckingAccount private[prop](no: String, name: String, openingDate: Date, closeDate: Option[Date]) 
  extends Account

// the smart constructor containing initialization logic
object Account {
  private val validDate: (Date, Date) => Boolean = { (d1, d2) => d1 before d2 }

  def checkingAccount(no: String, name: String, openingDate: Date, 
    closeDate: Option[Date] = None): Try[Account] = { 

    if (closeDate.map(validDate(_, openingDate)).getOrElse(false)) 
      Failure(new IllegalArgumentException(
        s"Account close date [$closeDate] cannot be earlier than opening date [$openingDate]")) 
    else Success(CheckingAccount(no, name, openingDate, closeDate))
  }
}

// generator
implicit val arbTAccount: Arbitrary[Try[Account]] = Arbitrary {
  for {
    no <- Gen.oneOf("1", "2", "3")
    nm <- Gen.oneOf("john", "david", "mary")
    od <- arbitrary[Date]
  } yield checkingAccount(no, nm, od)
}

// property
property("account open date < close date if close date is present") = forAll((a: Try[Account]) =>
  a match {
    case Success(acc) => acc.closeDate.map(cd => (acc.openingDate before cd) == true).getOrElse(true)
    case Failure(ex) => false == false
  }
)

The before logic is duplicated in both smart constructor and property, isn't it?

But that's the property you r proving. Hence you need to verify the same from the generated data. Instead of using acc.openingDate before cd you could use the validDate function also.