go-by-test/wallet/wallet_test.go

package wallet

import (
	"fmt"
	"testing"
)

func ExampleWallet() {
	wallet := Wallet{10}

	wallet.Deposit(10)
	fmt.Printf("The balance is %s\n", wallet.Balance())

	err := wallet.Withdraw(10)
	if err != nil {
		fmt.Println(err)
	}
	fmt.Printf("The balance is %s\n", wallet.Balance())

	// Output: The balance is 20 BTC
	// The balance is 10 BTC
}

func TestWallet(t *testing.T) {
	t.Run("deposit", func(t *testing.T) {
		wallet := Wallet{}
		wallet.Deposit(10)
		assertBalance(t, wallet, Bitcoin(10))
	})

	t.Run("withdraw", func(t *testing.T) {
		wallet := Wallet{balance: Bitcoin(20)}
		err := wallet.Withdraw(10)
		assertNoError(t, err)
		assertBalance(t, wallet, Bitcoin(10))
	})

	t.Run("withdraw insufficient funds", func(t *testing.T) {
		startingBalance := Bitcoin(20)
		wallet := Wallet{balance: startingBalance}
		err := wallet.Withdraw(100)

		assertError(t, err, ErrInsufficientFunds)
		assertBalance(t, wallet, startingBalance)
	})
}

func assertBalance(t testing.TB, wallet Wallet, want Bitcoin) {
	t.Helper()

	got := wallet.Balance()
	if got != want {
		t.Errorf("got %q, want %q", got, want)
	}
}

func assertError(t testing.TB, got error, want error) {
	t.Helper()

	if got == nil {
		t.Fatal("didn't get an error but wanted one")
	}
	if got != want {
		t.Errorf("got %q, want %q", got, want)
	}
}

func assertNoError(t testing.TB, got error) {
	t.Helper()

	if got != nil {
		t.Fatal("get an error but didn't want one")
	}
}