chore: add info about transparent referency

Author: damiengouyette

errormanagment/src/test/scala/ErrorManagementExceptionSpec.scala

@@ -1,50 +1,58 @@
 import org.scalatest.flatspec.AnyFlatSpec
 import org.scalatest.matchers.should.Matchers
 
+/**
+ * Referential transparency is a property of programming language expressions
+ * which means that an expression can be replaced by
+ * its value without changing the program's behavior.
+ *
+ * A pure function need Referential transparency
+ */
 class ErrorManagementExceptionSpec extends AnyFlatSpec with Matchers {
 
   trait AccountStatus
   case object Open extends AccountStatus
   case object Closed extends AccountStatus
+  case class BankAccount(availableMoney : Double, status : AccountStatus)
 
   class NegativeAmountException extends RuntimeException
   class InsufficientFundsException extends RuntimeException
   class AccountClosedException extends RuntimeException
 
-  case class BankAccount(availableMoney : Double, status : AccountStatus)
-  def withDraw(amount: Double, bankAccount: BankAccount): Unit = {
+  def withDraw(amount: Double, bankAccount: BankAccount): BankAccount = {
     if (amount < 0) {
       throw new NegativeAmountException
     } else if (amount > bankAccount.availableMoney) {
       throw new InsufficientFundsException
     }else if (bankAccount.status == Closed){
       throw new AccountClosedException
     }
+    bankAccount.copy(availableMoney = bankAccount.availableMoney-amount)
   }
 
-  "Withdrawing more money than the bank account holds" should " return false" in {
+  "Withdrawing more money than the bank account holds" should "throw a InsufficientFundsException exception" in {
     val emptyBankAccount = BankAccount(0, Open)
     assertThrows[InsufficientFundsException] {
       withDraw(amount = 20_000, bankAccount = emptyBankAccount)
     }
   }
 
-  "Withdrawing negative money" should " return false" in {
+  "Withdrawing negative money" should "throw a NegativeAmountException exception" in {
     val bankAccountWithMoney = BankAccount(10_000, Open)
     assertThrows[NegativeAmountException] {
       withDraw(-100, bankAccountWithMoney)
     }
   }
-  "Withdrawing on closed money" should "return false" in {
+  "Withdrawing on closed money" should "throw a AccountClosedException exception" in {
     val bankAccountWithMoney = BankAccount(200, Closed)
     assertThrows[AccountClosedException] {
       withDraw(100, bankAccountWithMoney)
     }
   }
 
-  "withdrawing money from an adequately funded account" should "return true" in {
+  "withdrawing money from an adequately funded account" should "return unit" in {
     val bankAccountWithMoney = BankAccount(10_000, Open)
-    withDraw(100, bankAccountWithMoney) shouldBe ()
+    withDraw(100, bankAccountWithMoney) shouldBe (BankAccount(9_900, Open))
   }
 
 }