add basic test for logger

I want a "pluggable" logger, but we need more tests beforehand ;-)
I would prefer if we could keep the tests from outputting to STDOUT - which is an interesting problem to solve in relation with logging tests, which is kind of expected to write to STDOUT sometimes :)

As far as this current test goes, it would probably be OK to add the following snippet somewhere around here:
```perl
no warnings 'once';
$::QUIET=1
```