diff --git a/wallet/wallet_test.go b/wallet/wallet_test.go
index cc66fa6..a0f7f89 100644
--- a/wallet/wallet_test.go
+++ b/wallet/wallet_test.go
@@ -8,15 +8,18 @@ func TestWallet(t *testing.T) {
 
 		got := wallet.Balance()
 		if got != want {
-			t.Errorf("got %q want %q", got, want)
+			t.Errorf("got %q, want %q", got, want)
 		}
 	}
 
-	assertError := func(t testing.TB, err error) {
+	assertError := func(t testing.TB, got error, want string) {
 		t.Helper()
 
-		if err == nil {
-			t.Error("wanted an error but didn't get one")
+		if got == nil {
+			t.Fatal("didn't get an error but wanted one")
+		}
+		if got.Error() != want {
+			t.Errorf("got %q, want %q", got, want)
 		}
 	}
 
@@ -37,7 +40,7 @@ func TestWallet(t *testing.T) {
 		wallet := Wallet{balance: startingBalance}
 		err := wallet.Withdraw(100)
 
-		assertError(t, err)
+		assertError(t, err, "not enough to withdraw")
 		assertBalance(t, wallet, startingBalance)
 	})
 }