buf := make([]byte, 3) // All runes in this test are 3 bytes long
	r := NewReader(&StringReader{data: []string{"日本語日本語日本語"}})
	if r.UnreadRune() == nil {
		t.Error("expected error on UnreadRune from fresh buffer")
	}
	_, _, err := r.ReadRune()
	if err != nil {
		t.Error("unexpected error on ReadRune (1):", err)
	}
	if err = r.UnreadRune(); err != nil {
		t.Error("unexpected error on UnreadRune (1):", err)
	}

	FCFIDU F1, F2                   // fc400f9c
	FCFIDUCC F1, F2                 // fc400f9d
	FCFIDS F1, F2                   // ec400e9c
	FCFIDSCC F1, F2                 // ec400e9d
	FRES F1, F2                     // ec400830
	FRESCC F1, F2                   // ec400831
	FRIM F1, F2                     // fc400bd0
	FRIMCC F1, F2                   // fc400bd1
	FRIP F1, F2                     // fc400b90