def calculateDiscount(customer: Customer, now: LocalDate): BigDecimal

case class Customer(
    name: String, 
    joinedAt: LocalDate, 
    dateOfBirth: LocalDate
)

  "Discount calculator" should "return 10% discount for a one year member" in {
    val dateOfBirth = LocalDate.of(1980, 1, 20)
    val customer = Customer("Sue Smith", NOW.minusYears(1), dateOfBirth)

    val discount = calculator.calculateDiscount(customer, NOW)

    discount should be(BigDecimal(0.1))
  }

  it should "return 20% discount for a two year member" in {
    val dateOfBirth = LocalDate.of(1980, 1, 20)
    val customer = Customer("Sue Smith", NOW.minusYears(2), dateOfBirth)

    val discount = calculator.calculateDiscount(customer, NOW)

    discount should be(BigDecimal(0.2))
  }

it should "return birthday discount" in {
  val customer = Customer("Sue Smith", NOW.minusYears(1), NOW.withYear(1980))

  val discount = calculator.calculateDiscount(customer, NOW)

  discount should be(BigDecimal(0.3))
}

it should "return no discount for a new member" in {
  val customer = Customer("Sue Smith", NOW, LocalDate.of(1980, 1, 20))

  val discount = calculator.calculateDiscount(customer, NOW)

  discount should be(BigDecimal(0))
}

it should "return 20% discount for a three year member" in {
  val dateOfBirth = LocalDate.of(1980, 1, 20)
  val customer = Customer("Sue Smith", NOW.minusYears(3), dateOfBirth)

  val discount = calculator.calculateDiscount(customer, NOW)

  discount should be(BigDecimal(0.2))
}

def calculateDiscount(customer: Customer, now: LocalDate): BigDecimal

case class Customer(
    name: String, 
    joinedAt: LocalDate, 
    dateOfBirth: LocalDate
)

property("Discount should not be over 30 percent") {
  forAll { (customer: Customer, now: LocalDate) =>
    val discount = calculator.calculateDiscount(customer, now)
    discount should be <= BigDecimal(0.3)
  }
}

ScalaTestFailureLocation: pbt.DiscountCalculatorPropertySpec at (DiscountCalculatorPropertySpec.scala:28)
org.scalatest.exceptions.GeneratorDrivenPropertyCheckFailedException: DateTimeException was thrown during property evaluation.
  Message: Invalid date 'February 29' as '2049' is not a leap year
  Occurred when passed generated values (
    arg0 = Customer(nWtCZLoAQ,2009-04-14,1988-02-29),
    arg1 = Customer(bLNkLdYmCYCjVJlIDRWumkWZceQHyoulrCcietBLPyfBCqbyXqub,2015-12-19,1996-12-13),
    arg2 = 2049-04-09
  )

Gen.choose(10, 99)

Gen.listOfN(5, Gen.alphaUpperChar)

Gen.uuid

Gen.option(Gen.oneOf("Home", "Work", "Other")

// (...)

val customerGen: Gen[Customer] = for {
    name <- Gen.alphaStr
    dateJoined <- dateFromRangeGen(START_OF_BUSINESS, LocalDate.now)
    dateOfBirth <- dateFromRangeGen(OLDEST_DAY_OF_BIRTH, LocalDate.now.minusYears(18))
  } yield Customer(name, dateJoined, dateOfBirth)
  
private def dateFromRangeGen(rangeStart: LocalDate, rangeEnd: LocalDate): Gen[LocalDate] = {
  Gen.choose(rangeStart.toEpochDay, rangeEnd.toEpochDay).map(i => LocalDate.ofEpochDay(i))
}

property("Birthday discount should be highest") {
  forAll { (customer: Customer, birthdayCustomer: Customer) =>
    val now = birthdayCustomer.dateOfBirth.withYear(2021)
      
    whenever(isNotBirthday(customer, now)) {
      val ordinaryDiscount = calculator.calculateDiscount(customer, now)
      val birthdayDiscount = calculator.calculateDiscount(birthdayCustomer, now)
      birthdayDiscount.compare(ordinaryDiscount) should be >= 0
    }
  }
}

property("End of presentation") {
  forAll { (attendee: Attendee) =>
    whenever(attendee.hasQuestions) {
      attendee.questionsAsked should be > 0
    }
  }
}