* mock get_str() is now via a fixture so it can be re-used in more than
one test, avoiding DRY issue.
* Some actual tests, in the form of asserts, added to
test_journal_lock_init().
In general I think this will keep things neater:
1. Create a directory inside tests/ named after the file the tests are
for.
2. Put all files for that test inside this new directory.