This file can be treated like the other index files in repo/. This also has
the advantage that it will automatically get synced by @CiaranG's existing
sync scripts.
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_
