func TestRuneIO(t *testing.T) {
	const NRune = 1000
	// Built a test slice while we write the data
	b := make([]byte, utf8.UTFMax*NRune)
	var buf Buffer
	n := 0
	for r := rune(0); r < NRune; r++ {
		size := utf8.EncodeRune(b[n:], r)
		nbytes, err := buf.WriteRune(r)
		if err != nil {
			t.Fatalf("WriteRune(%U) error: %s", r, err)
		}
		if nbytes != size {
			t.Fatalf("WriteRune(%U) expected %d, got %d", r, size, nbytes)
		}

		if b.Flush(); b.err != nil {
			return 0, b.err
		}
		n = b.Available()
		if n < utf8.UTFMax {
			// Can only happen if buffer is silly small.
			return b.WriteString(string(r))
		}
	}
	size = utf8.EncodeRune(b.buf[b.n:], r)
	b.n += size
	return size, nil
}

// WriteString writes a string.
// It returns the number of bytes written.
// If the count is less than len(s), it also returns an error explaining

			if r1 == utf8.RuneError {
				return i
			}
			i += n
		}
		return -1
	case !utf8.ValidRune(r):
		return -1
	default:
		var b [utf8.UTFMax]byte
		n := utf8.EncodeRune(b[:], r)
		return Index(s, b[:n])
	}
}

// IndexAny interprets s as a sequence of UTF-8-encoded Unicode code points.
// It returns the byte index of the first occurrence in s of any of the Unicode