pointers

pointers/wallet.go

@@ -0,0 +1,35 @@
+package wallet
+
+import (
+	"errors"
+	"fmt"
+)
+
+type Bitcoin int
+
+func (b Bitcoin) String() string {
+  return fmt.Sprintf("%d BTC", b)
+}
+
+type Wallet struct{
+  balance Bitcoin
+}
+
+func (w *Wallet) Deposit(amount Bitcoin)  {
+  w.balance += amount 
+}
+
+var ErrInsufficientFunds = errors.New("cannot withdraw, insufficient funds")
+
+func (w *Wallet) Withdraw(amount Bitcoin) error  {
+  if amount > w.balance {
+    return ErrInsufficientFunds
+  }
+
+  w.balance -= amount 
+  return nil
+}
+
+func (w *Wallet) Balance() Bitcoin {
+  return w.balance
+}

pointers/wallet_test.go

@@ -0,0 +1,51 @@
+package wallet
+
+import "testing"
+
+func TestWallet(t *testing.T) {
+  assertBalance := func(t testing.TB, wallet Wallet, want Bitcoin) {
+    t.Helper()
+    got := wallet.Balance()
+
+    if got != want {
+      t.Errorf("got %s want %s", got, want)
+    }
+  }
+
+  assertNoError := func(t testing.TB, got error) {
+    t.Helper()
+    if got != nil {
+      t.Fatal("got an error but didn't want one")
+    }
+  }
+
+  assertError := func(t testing.TB, got, want error) {
+    t.Helper()
+    if got == nil {
+      t.Fatal("wanted an error but didn't get one")
+    }
+
+    if got != want {
+      t.Errorf("got %q, want %q", got, want)
+    }
+  }
+
+  t.Run("deposit", func(t *testing.T) {
+    wallet := Wallet{}
+    wallet.Deposit(Bitcoin(10))
+    assertBalance(t, wallet, Bitcoin(10))
+  })
+  t.Run("withdraw with funds", func(t *testing.T) {
+    wallet := Wallet{balance: Bitcoin(20)}
+    err := wallet.Withdraw(Bitcoin(10))
+    assertNoError(t, err)
+    assertBalance(t, wallet, Bitcoin(10))
+  })
+  t.Run("withdraw insufficient funds", func(t *testing.T) {
+    startingBalance := Bitcoin(20)
+    wallet := Wallet{startingBalance}
+    err := wallet.Withdraw(Bitcoin(100))
+    assertError(t, err, ErrInsufficientFunds)
+    assertBalance(t, wallet, startingBalance)
+  })
+}