The tests relied on Python2 relative import semantics. Python3 changed
import semantics to always search sys.path by default. To import using a
relative path it must have a leading dot.
Forward compatible with newer Pythons.
Works towards the goal of moving tests outside of the installed package.
For more information, see PEP-328:
https://www.python.org/dev/peps/pep-0328/
There is no need to import testutils.unittest instead of simply
unittest. They are simple aliases. Use system unittest to be more
regular, consistent as well as idiomatic with the wider Python
community.
I'll be honest: I lucked out, I didn't think about this combination. But
maybe sheer luck, maybe using common code paths, it just works. Let's
make it stays so.
