implement transaction.go:Transaction:isRefund

digits-work-sample-go.d/transaction.go

@@ -24,7 +24,7 @@ type Transaction struct {
 }
 
 func (trn Transaction) String() string {
-	if trn.Amount < 0 {
+	if trn.isRefund() {
 		return trn.stringifyRefund()
 	}
 	return trn.stringifyExpense()
@@ -43,6 +43,10 @@ func (trn Transaction) stringifyCardholder() string {
 	return fmt.Sprintf("%s. %s", trn.CardholderFirstInitial, trn.CardholderLastName)
 }
 
+func (trn Transaction) isRefund() bool {
+	return trn.Amount < 0
+}
+
 // Transactions represents a list of Transaction
 type Transactions []Transaction