This test should ensure we correctly detect all invalid utf-8 sequences in a given string.
DISCLAIMER:
Do not run this with current code - you'll either laugh or cry, nearly *all* checks fail!
Based on utf-8 decoder stress-test (https://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-test.txt)
by Markus Kuhn <http://www.cl.cam.ac.uk/~mgk25/> - 2015-08-28 - CC BY 4.0