Which is why I've seen lots of people recommend testing your software with emojis, particularly recently-added emojis (many of the earlier emojis were in the basic multilingual plane, but a lot of newer emojis are outside the BMP, i.e. the "astral" planes). It's particularly fun to use the (U+1F4A9) emoji for such testing, because of what it implies about the libraries that can't handle it correctly.

EDIT: Heh. The U+1F4A9 emoji that I included in my comment was stripped out. For those who don't recognize that codepoint by hand (can't "see" the Matrix just from its code yet?), that emoji's official name is U+1F4A9 PILE OF POO.

For more fun you can use flag characters.