I'd prefer constructing this inside the test (with a subscoped directory name), along with the pipes below, and passing them explicitly to the helper functions that need them.

These sorts of global test instances seem to lead to a mess 🙂

Done, but for now, it still depends on the index being populated by the tbl in common.

index_name is defined above and subscoped to _tests. Is this what you meant?

If this test uses index_name to construct it's instance-under-test, future tests will also test the same instance on disk. I was suggesting doing something like this to make sure each test uses a unique name.

It's not a big deal, however, since my PR will clean up these sorts of details.

And w.r.t. the table being populated by Common: I'm also working on that 🙂