Saving withdraw feature

learn_go_with_tests/pointers_errors/wallet.go

@@ -1,6 +1,9 @@
 package pointers_errors
 
-import "fmt"
+import (
+	"errors"
+	"fmt"
+)
 
 type Stringer interface {
 	String() string
@@ -41,6 +44,10 @@ func (w *Wallet) Balance() Bitcoin {
 	return (*w).balance
 }
 
-func (w *Wallet) Withdraw(amount Bitcoin) {
+func (w *Wallet) Withdraw(amount Bitcoin) error {
+	if amount > w.balance {
+		return errors.New("Withdraw operation failed. Insufficient funds")
+	}
 	w.balance -= amount
+	return nil
 }

learn_go_with_tests/pointers_errors/wallet_test.go

@@ -1,27 +1,26 @@
 package pointers_errors
 
 import (
-	"fmt"
 	"testing"
 )
 
 func TestWallet(t *testing.T) {
 
-	t.Run("deposit", func(t *testing.T) {
-		wallet := Wallet{}
-
-		wallet.Deposit(10)
-
+	assertBalance := func(t *testing.T, wallet Wallet, want Bitcoin) {
+		t.Helper()
 		got := wallet.Balance()
 
-		// %p is placeholder for address in memory
-		fmt.Printf("address of balance in test is %p \n", &wallet.balance)
-		want := Bitcoin(10)
-
 		if got != want {
-			// t.Errorf("got %d want %d", got, want)
 			t.Errorf("got %s want %s", got, want)
 		}
+	}
+
+	t.Run("deposit", func(t *testing.T) {
+		wallet := Wallet{}
+
+		wallet.Deposit(10)
+
+		assertBalance(t, wallet, Bitcoin(10))
 	})
 
 	t.Run("withdraw", func(t *testing.T) {
@@ -29,11 +28,19 @@ func TestWallet(t *testing.T) {
 
 		wallet.Withdraw(Bitcoin(10))
 
-		got := wallet.Balance()
-		want := Bitcoin(10)
+		assertBalance(t, wallet, Bitcoin(10))
 
-		if got != want {
-			t.Errorf("got %s want %s", got, want)
+	})
+
+	t.Run("withdraw insufficient funds", func(t *testing.T) {
+		startingBalance := Bitcoin(20)
+		wallet := Wallet{balance: startingBalance}
+		err := wallet.Withdraw(Bitcoin(100))
+
+		assertBalance(t, wallet, startingBalance)
+
+		if err == nil {
+			t.Error("Wanted an error but didn't get one")
 		}
 
 	})