🐛 (bitcoin-wallet): add throw error logic for insufficient error

Author: yuanyu90221

pointers-and-errors/bitcoin-and-wallet.go

@@ -24,6 +24,10 @@ func (w *Wallet) Balance() Bitcoin {
 }
 
 // Withdraw - deposit amount from wallet balance
-func (w *Wallet) Withdraw(amount Bitcoin) {
+func (w *Wallet) Withdraw(amount Bitcoin) error {
+	if w.balance < amount {
+		return fmt.Errorf("oh no")
+	}
 	w.balance -= amount
+	return nil
 }

pointers-and-errors/bitcoin-and-wallet_test.go

@@ -29,4 +29,16 @@ func TestWallet(t *testing.T) {
 		want := Bitcoin(10)
 		assertBalance(t, wallet, want)
 	})
+
+	t.Run("withdraw insufficient funds", func(t *testing.T) {
+		startingBalance := Bitcoin(20)
+		wallet := Wallet{startingBalance}
+		err := wallet.Withdraw(Bitcoin(100))
+
+		assertBalance(t, wallet, startingBalance)
+
+		if err == nil {
+			t.Error("wanted an error but didn't get one")
+		}
+	})
 }