* It should include a subdir named after the test case.
* self.testdir is the common var name for this.
* tmp_repo is not a repo/ subdir, but instead the root of the whole repo
This name always confuses me, since there is also test_common.py. And this
module is not actually a test suite, even though it starts with "test".
This also makes for better tab completion, e.g.
python3 -m unittest tests/te[Tab] -> tests/test_