in   string
	repl string
	out  string
}{
	{"", "\uFFFD", ""},
	{"abc", "\uFFFD", "abc"},
	{"\uFDDD", "\uFFFD", "\uFDDD"},
	{"a\xffb", "\uFFFD", "a\uFFFDb"},
	{"a\xffb\uFFFD", "X", "aXb\uFFFD"},
	{"a☺\xffb☺\xC0\xAFc☺\xff", "", "a☺b☺c☺"},
	{"a☺\xffb☺\xC0\xAFc☺\xff", "日本語", "a☺日本語b☺日本語c☺日本語"},
	{"\xC0\xAF", "\uFFFD", "\uFFFD"},
	{"\xE0\x80\xAF", "\uFFFD", "\uFFFD"},
	{"\xed\xa0\x80", "abc", "abc"},