b.WriteString("gamma")
	check(t, &b, "alphabetagamma")
	s3 := b.String()

	// Check that subsequent operations didn't change the returned strings.
	if want := "alpha"; s1 != want {
		t.Errorf("first String result is now %q; want %q", s1, want)
	}
	if want := "alphabeta"; s2 != want {
		t.Errorf("second String result is now %q; want %q", s2, want)
	}
	if want := "alphabetagamma"; s3 != want {